Evaluating and Explaining Climate Science

Clouds and Water Vapor – Part One

In the CO2 series we looked at the effect of CO2 without climate feedbacks. The “answer” to the doubling of CO2 was a “radiative forcing” of 3.7W/m^2 and an increase in surface temperature of about 1°C.

What about feedbacks?

There are many ways to introduce this problem. We’ll start with the great Ramanathan, who is always worth reading. This article discusses the ideas in the chapter The Radiative Forcing due to Clouds and Water Vapor (by Ramanathan and Inamdar) from Frontiers of Climate Modeling by Kiehl and Ramanathan (2006). Note that the link allows you to download the chapter. Well worth reading.

And if you have questions about whether CO2 can influence temperature or whether the inappropriately-named “greenhouse” effect exists, take a look at the CO2 series (and ask questions there).

Preamble

Various papers from the 60’s onwards that attempted to model the change in radiative flux and surface temperature (as a result of changes in CO2 concentrations) usually solved the problem using (at least) two scenarios:

constant absolute humidity

constant relative humidity

The reason is that absolute humidity is less realistic than relative humidity – and the concept of relative humidity leads to positive feedback. Why positive feedback? Higher concentrations of CO2 lead to increased radiative forcing and so the surface and tropospheric temperature increases. As a result – under constant relative humidity – the amount of water vapor in the troposphere increases. Water vapor is a greenhouse gas and so further increases “radiative forcing”.

One of the questions that come to people’s minds is whether this leads to thermal runaway. The answer, when considering the “extra” effect from water vapor is no, and this is because there are also negative feedbacks in the system, especially the fact that radiation (a negative feedback) increases as the 4th power of absolute temperature.

But enough of trying to think about the complete solution before we have even begun. Let’s take the time to understand the thinking behind the problem.

Cloudy Skies

Clouds are one of the toughest problems in climate science, and as a result, many models and experiments differentiate between cloudy and clear skies.

Clouds reflect solar radiation by 48 W/m2 but reduce the outgoing longwave radiation (OLR) by 30 W/m2, therefore the average net effect of clouds – over this period at least – is to cool the climate by 18 W/m2. Note that these values are the global annual average.

Here are the net shortwave (solar reflection) and net OLR effects from clouds over the whole period:

and the two effects combined:

The “Greenhouse” Effect and Water Vapor

I’ll try and keep any maths to a minimum, but a few definitions are needed.. if you don’t like seeing equations the explanations in the text mean you haven’t missed anything essential.

We will call the “greenhouse” effect of the atmosphere and clouds, G, and the average OLR (outgoing longwave radiation), F:

F = σTs4 – G

The first term on the right-hand side of the equation, σTs4, is just the radiation from the earth’s surface at a temperature of Ts (the Stefan-Boltzmann equation). So the radiation from the earth’s surface less the “greenhouse” effect is the amount of radiation that escapes to space.

G is made up of the clear sky “greenhouse” effect, Gclear, and the (longwave) effect of clouds, Gcloud.

Now as we move from the hotter equator to the colder poles we would expect Gclear to reduce simply because the surface radiation is much reduced – a 30°C surface emits 480 W/m2 and a 0°C surface emits 315 W/m2. A large proportion of the changes in the “greenhouse” effect, Gclear, are simply due to changes in surface temperature.

Therefore, we introduce a normalized “greenhouse” effect, gclear:

gclear = Gclear / σTs4

This parameter simply expresses the ratio between the clear sky “greenhouse” effect and the surface radiation. The variations in this normalized value reflect changes in atmospheric humidity and lapse rates (the temperature profile up through the atmosphere). See especially CO2 – An Insignificant Trace Gas? Part Five for a little more illumination on this.

The global average value for Gclear = 131 W/m2 and for gclear = 0.33 – i.e., the atmosphere reduces the radiation escaping to space by 33%.

Here is how gclear varies around the world (top graphic) compared with water vapor around the world (bottom graphic):

It should be clear from these graphics that observed variations in the normalized “greenhouse” effect are largely due to changes in water vapor. [Note – change of notation from the graphics – ga in the graphic is gclear in my text]

Water vapor decreases from equator to pole due to temperature (lower temperatures mean lower absolute humidity), and increases over ocean compared with land (because of the availability of water to evaporate).

Feedback

If we can see that the “greenhouse” effect is strongly influenced by water vapor, we want to know how water vapor changes in response to surface and tropospheric temperature changes.

To make sense of this section it’s helpful to follow some maths. However, I recognize that many people would rather skip any maths so this is in the last section for reference.

Here are the results from ERBE for: the tropics (30°N – 30°S) with surface temperature; the “greenhouse” effect + the normalized version; and the change in water vapor in different vertical sections of the atmosphere:

Ramanathan says:

For the tropics, Ts peaks in March/April, while for 90°N–90°S, Ts peaks in July. We can qualitatively interpret the phase of the annual cycle as follows. The tropical annual cycle is dominated by the coupled ocean–atmosphere system and as a result, the temperature response lags behind the forcing by a maximum of about three months (π/2); thus, with the solar insolation peaking in December 21, the temperature peaks in late March as shown in Figure 10.

Now the whole globe as a comparison:

Ramanathan again:

The extra-tropical and global annual cycle is most likely dominated by the hemispherical asymmetry in the land fraction. During the northern-hemisphere summer (June, July, and August), the large land masses warm rapidly (with about a one month lag) which dominates the hemispherical and global mean response; however, during the southern-hemisphere summer, the relatively smaller fraction of land prevents a corresponding response. Thus, the globe is warmest during June/July and is coldest during December/January.

What can we make of the correlation? Correlation doesn’t equal causation.

The best fit is a phase lag of less than a month which implies that water vapor and gclear are not driving Ts – because the feedback in that case would require more than one month. The converse, that Ts is driving water vapor and gclear, is much more likely because convective time scales are very short.

Of course, this is a deduction from a limited time period.

One of the key relationships in understanding feedback is the change in Gclear with Ts (mathematically we write this as dGclear/dTs – which means “the rate of change with Gclear as Ts varies “).

For reasons briefly outlined in the maths section, if dGclear / dTs > 2.2 it implies positive feedback from the climate.

When the data is plotted from the ERBE data we can see that in the tropics the value is the highest, much greater than 2.2, and when the whole globe is included the value reduces significantly. However, the value for the whole globe still implies positive feedback.

In this last graph we see the feedback value for progressively wider latitude ranges – so on the left we are only looking at the tropics, while over on the right (90°N to 90°S) we are looking at the entire planet. This helps to see the contribution from the tropics progressively outweighed by the rest of the plant – so the important point is that without the strong effect from the tropics the feedback might well have moved to negative.

The feedback doesn’t change between clear sky and all sky, implying that the cloud feedback doesn’t impact the climate system feedback (on these timescales).

Ramanathan comments:

However, our results do not necessarily confirm the positive feedback resulting from the fixed relative humidity models for global warming, for the present results are based on annual cycle. We need additional tests with decadal time-scale data for a rigorous test. Nevertheless, the analysis confirms that water vapor has a positive feedback effect for global-scale changes on seasonal to inter-annual time scales.

He also comments on other work (including Lindzen) that finds different results for the relative important of water vapor in different vertical sections of the troposphere.

Hopefully, we will get the opportunity to consider these in future articles.

Part Six – Nonlinearity and Dry Atmospheres – demonstrating that different distributions of water vapor yet with the same mean can result in different radiation to space, and how this is important for drier regions like the sub-tropics

Conclusion

This is a big subject which has lots of different perspectives, and only one is developed here. Therefore, I hope that this is the first of many articles on the subject.

It should be helpful to see the approach and one way of interpreting the data. There is a theoretical framework behind the concepts, which can be seen in Ramanathan’s paper from 1981: The Role of Ocean-Atmosphere Interaction in the CO2 Climate Problem. (You can find a free copy online). It’s quite involved but perhaps some of the concepts from this paper will be in one of the next posts in this series.

Maths

I’ll follow the notations from the chapter reasonably closely. But I think they are confusing so I have changed a few of them.

And if you do want to understand the maths it’s definitely worth taking a look at the more detailed explanations in the chapter to understand this beyond the surface.

F = OLR (outgoing longwave radiation)

F = Fclear (1-f) + f.Fcloudy, where f is the fraction of clouds, and Fclear is the clear sky OLR

F = σTs4 – G [1], where G is the “greenhouse” effect

and G = Gclear + Gcloud [2]

Now the main feedback parameter is dF/dTs, so:

dF/dTs = 4σTs3 – dG/dTs = 4σTs3 – (dGclear/dTs + dGcloud/dTs) [3]

Note that 4σTs3 = 5.5 Wm-2K-1 (at T=289K)

Background: dGclear/dTs is affected by water vapor and lapse rate and dGcloud/dTs is affected by cloud feedback and lapse rate

Now dGclear/dTs = 4σTs3 – dFclear/dTs [4]

now for Ts changing with no lapse rate feedback and no water vapor feedback, dFclear/dTs = 3.3 Wm-2K-1 (from Ramanathan 1981, see ref above in conclusion).

Like this:

Related

157 Responses

a 30°C surface emits 480 W/m2 and a 0°C surface emits 315 W/m2. A large proportion of the changes in the “greenhouse” effect, Gclear, are simply due to changes in surface temperature.

I ask how much the effect of relatively opaque atmosphere directly above the surface (soil?) affects the actual emission?

Asides from such complexities of emissivity of different surface types – e.g. snow vs trees vs pasture vs desert – how does the immediately lower atmosphere moderate the emission of energy?

In particular the difference in emissivity of the surface at Tsurface, with emissivity Esurface, compared to – say – the atmosphere in close proximity to the surface Tatmos, Eatmos?

I’ve asked before about equivalent mean-free-path of LR radiation in the lower atmosphere.

If we have the situation where energy from the surface (soil) is very quickly absorbed and re-emitted by the lower atmosphere, then the surface emissivity and temperature becomes quite irrelevant compared to t he atmospheric emissivity and temperature.

So I ask – perhaps in a different way – whether energy emission from the surface has any effect on energy eventually radiated by the atmosphere?

I expect that some energy from the surface will escape to space unhindered because it is not trapped by the atmosphere. I expect also that a large portion will interact with the atmosphere many times and that the resultant energy flux is not a function of surface emissivity and temperature, but of intermediate atmospheric layers.

SoD is this understanding correct? if so, how does it affect your explanation of radiative transfer from the soil to the sky?

At the opening of this post, ScienceOfDoom distorted the results of a previous post. In that post, you calculated that the radiative forcing associated with a doubling of CO2 (3.7 W/m^2) would increase temperature by 1.1 degC. In this post, you now claim that SURFACE temperature will increase by 1.1 degC. However, radiative forcing is defined as the change in energy flux at the tropopause, so your CALCULATED TEMPERATURE RISE IS ONLY CORRECT AT THIS ALTITUDE. This is also an altitude where convection plays relatively little role in convective-radiation equilibrium and a location where incoming and outgoing radiation may truly be in a state of near equilibrium that is not greatly perturbed by convection.

To use the radiative-convective model to calculate how SURFACE TEMPERATURE will change, one needs to know how doubling CO2 will change the lapse rate. If the lapse rate changed 0.1 degC/km (2%) and the tropopause is about 14 km above the surface, the radiative-convective equilibrium theory would predict a surface temperature rise of -0.3 to 2.5 degK depending on which way the lapse rate changed. Without knowing how lapse rate changes, one can NEVER use radiative-convective equilibrium to predict surface temperature changes associated with GHG increases.

The problem with radiative-convective equilibrium is that everyone at some point choses to ignore the possibility of changes in lapse rate (convection) and pretends that radiative forcing tells the whole story for SURFACE temperature. The radiative-convective theory you have presented so far is only based on first principles of physics ONLY at high altitudes and an assumption – fixed lapse rate – that more sophisticated models (3D-GCM’s) suggest is wrong. These models suggest that the lapse rate will increase (from a less negative number), reducing the impact of your calculated 1.1 degC temperature increase at the tropopause.

(For a proper calculation, 3.7 W/m^2 for 2X CO2 should be added to the downward flux at the tropopause, not a flux calculated by other means. One can calculate the total flux from temperature only by assuming convection is negligible.)

Clouds reflect solar radiation by 48 W/m2 but reduce the outgoing longwave radiation (OLR) by 30 W/m2, therefore the average net effect of clouds – over this period at least – is to warm the climate by 18 W/m2.

Since the reflected radiation is greater than the obtructed OLR, shouldn´t the net effect be to cool the climate by 18 W/m2 ?

How long does temperature take to respond to a radiative forcing? I think there must be different lags for atmosphere, land and ocean… Roughly how large are these lags?

I take the calculated forcings here refer to the 5-year time scale of the data. Would the results be much different for longer periods? Roughly how much?

“The five-year global mean energy budgets for clear and cloudy regions are illustrated in Figure 5.4. Clouds reduce the absorbed solar radiation by 48 W m−2(Cs = −48Wm−2) while enhancing the greenhouse effect by 30Wm−2 (Cl = 30Wm−2), and therefore clouds cool the global surface–atmosphere system by 18Wm−2(C = −18Wm−2) on average. The mean value of C is several times the 4Wm−2 heating expected from doubling of CO2 and thus Earth would probably be substantially warmer without clouds.”

In general temperature lags annual forcing over the oceans by about 60 days, but it is highly variable. Over land it varies by climate type. If the land climate is maritime it is much the same as the nearby ocean, if it is continental it is as little as ~3 weeks.

Now given that for most of the earth, the ocean, it lags from about 7 weeks to about 10 weeks, how come the average is only about a month.

Well, short lags are correlated with large temperature ranges so they dominate the average if you sum the temperatures and then work out the lag.

Were you to work out the lag for each cell on a gridded earth and average the lags, you would end up with a figure closer to two months for the non-equatorial regions. For the equatorial belt, the annual lag is a bit meaningless as the primary forcing signal is semi-annual.

So the average is around one month but the typical local value is more like two months.

So all these lags are way shorter than those 5 years, and the measurement, in principle, comprehends the full warming due to the forcing.

I understand, then, that the slower feedbacks are chemical or physical processes that are not direct responses to the forcing, but instead slower responses to the temperature itself – like the ocean release of CO2.

If I understand it right, the Charney sensitivity covers more than the radiative forcing and water vapor feedback.

Clouds reflect solar radiation by 48 W/m2 but reduce the outgoing longwave radiation (OLR) by 30 W/m2, therefore the average net effect of clouds – over this period at least – is to warm the climate by 18 W/m2. Note that these values are the global annual average.

I sincerely hope that this is a typo on your part, scienceofdoom. Because if not, then you are way off base. Clouds cool the earth, they don’t warm it.

Since the issue is not resolved that the temperature in the upper troposphere has increased, and the relative humidity has not stayed nearly constant (it has clearly decreased) over the period of greatest lower troposphere temperature increase, the argument seems less than resolved. The lack of increased water vapor in the stratosphere pushes that point even further. Finely, the data and analysis of Roy Spencer seems to lead to different conclusions even on the data interpretation. Can you point out his errors and respond to those issues?

I guess I need some serious tutoring, because none of this computes for me. The Kiehl Trenberth radiation balance cartoon shows a “back radiation” of 324 wm-2. I always thought that this “back radiation” IS the “greenhouse effect” incarnate! And the 324 watts is supposed to be ONLY the “average” for the planet. But now you tell me that the total maximum “greenhouse effect” for the TROPICS is only 168 wm-2? Why is it not at least equal to the average of 324? Where did I go wrong?

The “greenhouse value” as described by Ramanathan is the difference between the OLR (the top of atmosphere outgoing radiation) and the terrestrial radiation.
Top of atmosphere (upwards longwave), about 240W//m^2
Surface (upward longwave), about 390W/m^2
Difference = about 150W/m^2

This is a different value from the radiation from the atmosphere that we measure at the surface.

scienceofdoom,
May I make a suggestion. If you put the comments access at the beginning of the blog, or leave more space at the end between previous blogs, it would be easier to comment. Your blogs are long and run together, so scrolling down for finding the ends to comment is tedious. Possibly better would be to start a blog, then have a continue input to another site. Then the space between blogs would be easy to see, and comments easier to input.

Also the writer doesn’t appear to be clear about the difference between emissivity of a body (a blackbody has an emissivity of 1) for radiation and thermal capacity of a body. A surface can have both, the concepts aren’t in opposition.

Lastly, the writer hasn’t explained why radiation from the surface is so much higher than radiation from the top of atmosphere. See CO2- Part Six – Visualization

Having spent many years trying to improve the performance of amplifiers with a variety of feedback loops I am all too well aware of the technical difficulties even in situations which allow open loop gain/phase measurements to be made. In the case of the Earth’s climate there are many feedbacks, both positive and negative and there is no way to make open loop measurements.

Just to take one simple example you point out (probably correctly) that rising temperatures increase the amount of water vapor (a “Greenhoue” gas) in the atmosphere, constituting an added positive feedback. However, increased water vapour is also likely to increase cloud cover in the higher latitudes. The increased cloud cover should be a negative feedback. Then again, melting ice caps should be another positive feedback but one with a much longer time constant.

I was a little surprised to find that the great Ramanathan could ascribe the fact that January is cooler than July owing to more land in the northern hemisphere without mentioning the 16W/sq. meter radiative forcing due to the eccentricity in Earth’s orbit.

However, increased water vapour is also likely to increase cloud cover in the higher latitudes. The increased cloud cover should be a negative feedback..

The feedbacks are very complex and hard to unravel. As Ramanathan says, We need more data..

I was a little surprised to find that the great Ramanathan could ascribe the fact that January is cooler than July owing to more land in the northern hemisphere without mentioning the 16W/sq. meter radiative forcing due to the eccentricity in Earth’s orbit.

I guess it’s considered “well known”. There’s a lot of papers already just on “Milankovitch” that work through those points.

The Earth is closest to the sun in early January (TOA corrected for spherical geometry 353.4 W/m2) and furthest in July (330.5 W/m2) so, all other things being equal, one would expect peak temperature to occur no later than April. But of course all other things aren’t equal. The NH temperature range is ~10 K from min to max while the SH temperature range, 180 degrees out of phase with the NH, is ~6 K from min to max. So when you add the two together, the peak is in July. The effect of orbital eccentricity is swamped by the difference in land area in the two hemispheres.

That someone asking similar questions would be me. This post on clouds is very timely because even if extra 2xCO2 can produce a warming of 1C, the feedbacks may mitigate that warming from the extra CO2. There was a controversy about this recently when Monckton visited Australia and referred to the Pinker paper:

Pinker’s main interest was SW flux at TOA and BOA and between 198-2001 there appeared to be a net inward SW at TOA and an equivalent inward SW at the surface; in her paper Pinker refers to cloud variation as being the possible mechanism for this. Unfortunately Monckton misunderstood cloud forcing involved both the SW top of clouds effect and the bottom LW effect and the more fundamental point was lost in the discussion.

The point is this; if there is slight warming from CO2 then ET increases and so does cloud cover returning the ‘system’ to equilibrium; that is not a warmer equlibrium as predicted by AGW but close to the original one assuming no variation in external factors such as the sun.

I’ve struggled with conceptualizing the net effect of clouds a bit myself, but I’ve come to a different current understanding. I’ve had interesting conversations with people who follow the same path that you do, and I have to admit, some points can’t be argued with. For example, there is more water vapor when it is warmer and there are more clouds when there is more vapor. Physics and my own experience agree that clouds make for cooler days, but also warmer nights. What is the net effect? Water vapor is a GHG and so would enhance a warming forcing, but then more clouds would have some additional effect; so, how does this all balance out? I suspect you may be getting too caught up in the trees to see the forest.

Until the ERBE, I conceptualized it as follows: Let’s imagine that prior to widespread use of fossil fuels, the fluxes of water vapor were in some sort of equilibrium zone. The balance of water vapor in air where air and water are in contact is largely determined by the temperatures of the air and water. There’s a lot of ocean; so, let’s say that to a first order of magnitude, the amount of water vapor in the atmosphere is a function of the overall temperature of the system. (Other factors remaining approximately constant.) If the temperature falls, water precipitates out, if it rises, more water evaporates. What you are suggesting is a system where a) the cooling effect of clouds during the day is larger than the warming effect at night plus the warming effect of water vapor, and b) a system where water evaporates do to a warming, and then stays in suspension, does not precipitate, after a cooling.

If the system behaved the way you suggest, the climate would be strongly self-regulating. If that were the case, what would be the size of forcing(s) needed to create the past climates, both warmer and cooler ones than present? I suspect that they would have to be substantially larger than there is evidence to suggest.

The ERBE results suggest that clouds do indeed have an overall cooling effect, but the warming effects of water vapor outweigh the cooling effects of clouds. I’m hanging my hat there until something stronger comes out.

If we have the situation where energy from the surface (soil) is very quickly absorbed and re-emitted by the lower atmosphere, then the surface emissivity and temperature becomes quite irrelevant compared to the atmospheric emissivity and temperature.

Not really irrelevant – surface emissivity and temperature determine the radiation from the surface. This is the main “input” into this part of the climate process.

Do you think that that halving the radiation (for example) would have no effect?

So I ask – perhaps in a different way – whether energy emission from the surface has any effect on energy eventually radiated by the atmosphere?

The radiative transfer equations reveal that the answer is yes. And the measurements of OLR at different points around the globe confirm this.

“Also the writer doesn’t appear to be clear about the difference between emissivity of a body (a blackbody has an emissivity of 1) for radiation and thermal capacity of a body. A surface can have both, the concepts aren’t in opposition.”

I wonder if this is correct. No allowance seems to be made for heat storage in the greenhouse gas theory. The only focus is on radiation. I think that’s wrong.

You did not speak to the real heart of the paper: why are all the planets (and the moon) hotter than they “should be” considering only BB radiation.

Here’s a graph of the temperature response at the equator of a gray body (albedo 0.078) with a zero heat capacity, zero heat conductivity surface and of a body with moon-like heat capacity and zero horizontal heat conductivity surface.

I say moon-like because I didn’t use a diffusive vertical heat conductivity surface. The real moon, with a diffusive surface, heats up and cools somewhat faster, but the minimum temperature is about the same. The average temperature of the two bodies is quite different. The zero heat capacity surface has an average temperature at the equator of 167.2 K and the moon-like surface average is 219.6. The global average for the moon-like body is a little lower at ~207 K. The zero heat capacity global average should drop by about the same amount. A superconducting infinite heat capacity body with the same albedo has a constant temperature everywhere of 273.1 K

“why are all the planets (and the moon) hotter than they “should be” considering only BB radiation.”

Do you think it is valid to conclude that _the_ Moon is hotter than expected by measuring the temperature at a single location?
All this shows is that even on the moon you can’t use the black-body approximation to accurately calculate local temperatures.

Ironically one of the sources [10] he cites to show that planets are warmer than they should be, makes it quite clear that the observed temperatures on Mars are due to the effectiveness of CO2 as an absorber:
“So…40% of the energy is absorbed on its way from the ground out to space on Earth – at Venus this is 98%! but only 17% at Mars – seems a little but still half of the percentage of Earth even though Mars’ atmospheric pressure is only 0.6% of a bar – shows how CO2 is an effective absorber”

“Water vapor decreases from equator to pole due to temperature (lower temperatures mean lower absolute humidity), and increases over ocean compared with land (because of the availability of water to evaporate).”

Missing from this explanation is any reference to dynamics.

To be sure, the cold poles are drier than the warm tropics.

But the same cold poles produce cold air masses which lead to
the inter tropical convergence zone (ITCZ). The tropical belt maximum
is then partly thermodynamic and partly fluid dynamic.

It is quite instructive to watch week long animations of precipitable
water and follow polar air masses, marked by a distinct minima. These masses do modify, but slowly even as they reach the tropics,
traverse westward by the ITCZ across the oceans
(especially the Atlantic) and eventually return poleward. The ITCZ
is bounded by such masses from each hemisphere.

This motion appears to explain the “S” shaped contours in figure 5.8b
above in the Eastern ocean basins.

The other point, which you may be planning on addressing in future parts, is that for the recent decades’ warming, the best in situ data set,
indicates a negative water vapor feedback, not positive.

Water vapor seems to be a mixed bag depending on where it is concentrated; it would be good to get some definitive answer about whether SH and RH levels are declining, increasing or are stable; NOAA’s NCEP Reanalysis finds a decline as does Paltridge and Soloman while Dessler and others find the opposite.

The question of lags in the system is interesting; Ramanathan notes that they are short, 1-3 months which is agreement with Trenberth:

On my comment: “Also the writer doesn’t appear to be clear about the difference between emissivity of a body (a blackbody has an emissivity of 1) for radiation and thermal capacity of a body. A surface can have both, the concepts aren’t in opposition.”

Said:

I wonder if this is correct. No allowance seems to be made for heat storage in the greenhouse gas theory. The only focus is on radiation. I think that’s wrong.

If the only concept in atmospheric physics was radiation then yes it would be wrong. Radiation is one component. Usually textbooks on atmospheric physics build on basic physics including (not limited to) conduction, convection and radiation – they are kind of taken as read with a minimal introduction.
See, for example, Elementary Climate Physics by Prof FW Taylor, look at the contents section. Or check any other basic book on climate physics.

GCMs also, for all their faults, do consider the basics of heat conduction and convection as well as radiation.

I’m not sure where you get this idea.

You did not speak to the real heart of the paper: why are all the planets (and the moon) hotter than they “should be” considering only BB radiation

The real heart of the paper was about the moon without an atmosphere (not the planets) and demonstrated – assuming that what it produced was accurate, an assumption I don’t want to make because the writer makes basic errors at the start –

– that the surface of the moon stores some heat, therefore the climate is moderated. Like the oceans vs the land. This would be expected..

The writer says:

Thus (within the zone in question) the surface of the real moon is
roughly 20° cooler than predicted by day and 60° warmer by night, the net result being a surface that is
40° warmer than predicted

Predicted by whom?

This is somehow at odds with the basic theory of radiation? or at odds with atmospheric physics? Or disproves the inappropriately-named “greenhouse” theory?

Is the writer saying that atmospheric physics can’t explain the temperature of the moon?

If I understand the logic behind the Moon-argument correctly it goes like this:
– NASA has predicted the temperature curve for a landing spot based on the black body model
– the temperatures that they actually measured was on average higher than calculated (higher during the lunar night, lower during the day)
– the Moon has no atmosphere (i.e. no greenhouse effect)
– somebody at NASA looked into this and found that heat storage in the lunar soil needs to be taking into account to get the temperature right
– therefor climate scientists have obviously not considered heat storage in the Earth’s ground when they postulated their greenhouse-theory. If the Moon is doing it without an atmosphere, so must the Earth.

Science can be so gratifying if you don’t have to deal with real world measurements.

The whole point of the ilovemyco2 article has nothing at all to do with the “greenhouse” theory.

Any surface has a heat capacity. But supposing infinitesimal heat capacity, all of the radiation absorbed will be radiated back out immediately.

And the temperature of that surface will be such that E=emissivity x sigma x T^4,
where E is energy radiated in J/s, T is absolute temperature and sigma is 5.67×10^-8

And this temperature curve will follow the incoming radiation with no time lag.

(This seems to be the “theoretical” curve in that confused article)

With a heat capacity, the surface will “smooth” out the highs and lows, in exactly the same way as you find that continental interiors have much colder and hotter seasonal changes and diurnal changes compared with oceans and maritime climates.

And with this heat capacity the temperature curve will follow the incoming radiation with a time lag – because it takes time to heat up a body with a finite heat capacity -and it takes time to cool down a body with a finite heat capacity.

And the fact that a surface/body has a heat capacity says nothing about its emissivity or absorptivity of radiation.

The absorptivity tells you how much radiation it absorbs as a proportion of the total (the rest is reflected) and the heat capacity tells you how long it takes to heat up (by way of how many joules it takes to increase the temperature by 1K).

Whether NASA was once confused about the heat capacity of the surface of the moon I have no idea.

But it has nothing to do with the “greenhouse” theory.

And doesn’t explain why the surface of the earth is radiating (a global annual average ) of 396W/m^2 while the atmosphere is radiating at 239W/m^2.

Or why the surface of the earth receives downward radiation from the atmosphere with energy concentrated in wavelengths that correspond to the absorption spectra water vapor, CO2, CH4, O3 and NO2.

The heat capacity of the earth’s surface or of the ocean doesn’t actually explain this.

Folks: I think you are all completely missing the point of the article about the moon. It IS, in fact, addressing the greenhouse effect. We are constantly told that the SB calculations show that the Earth “should be” 33 C colder than it is. This supposedly proves that the “excess temperature” is due to a greenhouse effect. The article simply shows that heat storage can explain why the moon (and other planets) are higher than the flawed SB calcs. show. No need for a greenhouse effect. Read some of his references, also.

The fact that there is more radiation at the surface than at TOA can also be explained by the storage of heat in the atmosphere.

Earth absorbs 239wm-2 sunlight. Assuming a blackbody the surface should be about 255K. But Earth’s mean surface surface temperature is about 288K – greater than blackbody. That’s the key point about SB applied to Earth.

The moon is receiving about 295wm-2 sunlight. Assuming a blackbody the moon’s mean surface temperature should be about 269K. But is the moon’s temperature, like the Earth, greater than blackbody? Ie greater than 269K? The ilovemyco2 article doesn’t provide any estimate but if those day-night graphs are anything go on the average is lower than 269K.

We are constantly told that the SB calculations show that the Earth “should be” 33 C colder than it is. This supposedly proves that the “excess temperature” is due to a greenhouse effect.

“We are constantly told”? It’s foundational thermodynamics. Planck’s law, which you can see in The Sun and Max Planck Agree, when integrated over all wavelengths produces the Stefan-Boltzmann equation.

Max Planck won his Nobel prize for his great work in explaining black body radiation. If you can prove him wrong you will definitely win yours.

Any basic foundation course in heat transfer will teach you that there are three mechanisms: conduction, convection and radiation. Each one has to be considered in calculating the temperature change and heat flow in a system. Take a look at a thermodynamics book, you can probably find a few on google books, at least to see the contents page.

All the author of the ilovemyco2 article has done is demonstrate he knows nothing about the subject.

Why?

Because every single calculation of temperature change and heat transfer has to consider all mechanisms. It doesn’t invalidate the Stefan-Boltzmann equation or Planck’s law that conduction into the surface also takes place. These simply explain the local time-based response of the surface.

It’s like saying that the ocean is cooler than the desert during the day and warmer at night also demonstrates that the Stefan-Boltzmann equation and Planck’s law are wrong. Or any other arbitrary fact.

The fact that there is more radiation at the surface than at TOA can also be explained by the storage of heat in the atmosphere

How can it be explained exactly? The radiation is absorbed by the atmosphere?

Yes, that’s the “greenhouse” effect. And in absorbing energy the absorbing gases share this energy with all other local gases via collision. This part of the atmosphere radiates (according to temperature – Planck’s law and according to each molecule’s ability to radiate at each wavelength) in all directions.

That’s why we measure less leaving the atmosphere at the top and also downward radiation at the surface.

What’s your mechanism for radiation being “stored” without being absorbed and re-radiated?

You could be up for two Nobel prizes.

But, in the hope that you want to learn some basics I will do another article in the next few days that explains a few basics about conduction, convection and radiation.

Do you think the surface of the moon doesn’t radiate according to the Stefan-Boltzmann law?

Ie. E = emissivity x sigma x T^4 is not what is happening?

If we measure the temperature of the surface and know the emissivity then the radiation will not be according to this law?

Is that what you are thinking?

if it is..

No, the surface will be radiating exactly according to that law.

The issue in the iloveco2 article is the prediction of temperature. Let’s suppose that Nasa was once confused, or is even still confused about the specific heat capacity and conductivity of the moon’s surface.. and therefore can’t predict the temperature at any one time.

Actually it doesn’t solve your problem. Because if we measure the moon’s surface temperature at any instant and any point and measure the radiation emitted from that surface it will still match Planck’s law and therefore Stefan-Boltzmann’s law (or the Nobel will be yours).

And this is exactly what is done for the surface of the earth. The actual temperature of the earth and its emissivity are used to calculate the radiation from each point on the surface to calculate the average upward radiation. We don’t have to predict what the surface temperature will be, we just measure it.

And therefore the radiation from the surface averaged globally and annually is 396W/m^2.

Although it’s not done at thousands of stations many times per day as for temperature, it’s similar for atmospheric radiation. FT-IR spectrophotometers (see here for example: http://www.arm.gov/instruments/aeri )are pointed at the sky and spectra are recorded. These spectra are in very good agreement with spectra calculated with line-by-line programs using atmospheric soundings of temperature and humidity as input. Even lower resolution RT programs such as MODTRAN give reasonable agreement with the observed spectra.

OK; A_A=E_D and the size of S_T aside, the flux figures for surface radiating of 396w/m2 and atmosphere radiating 239w/m2 leave 157w/m2 for the greenhouse; the greenhouse effect mainly comes about through collisional transfer of the ‘energy’ absorbed by CO2 [primarily] to the bulk gases of the atmosphere, N2 and O2. Problems I still have include:

1 What causes Mars to be warmer than black body SB calculations show given the atmosphere is 95% CO2 with effectively no other gases to collisionally transfer energy to?
2 DeWitt has answered some of my concerns about the gas giants but the greenhouse effect on Venus still seems problematic considering it appears to have an internal heating source in the form of massive volcanic activity.
3 If pressure does not contribute to the 33C greenhouse temperature of Earth what part of the 33C is attributable to CO2?
4 Following on from 3, what effect does the log decline in the temperature effect of CO2 have?
5 Is the log decline increased by entropy?
6 Is backradiation occuring at clear night conditions in the usual day spectrum?
7 Does cointegration and unit root analysis undermine any CO2/temperature correlation and therefore greenhouse argument?

1. Collisional transfer occurs to other CO2 molecules. A collision of an excited molecule with another molecule that’s not excited usually results in two molecules in the ground state with somewhat higher kinetic energy but below the excited state. The percentage of CO2 molecules in the first excited state for the 15 micrometer bending mode is small, ~7% at 300 K, so there are still lots of CO2 molecules at lower energy to collide with. As long as energy transfer by collision is much more probable than radiation, the gas can be said to be at local thermal equilibrium and Kirchhoff’s Law applies.

2. I’m not that familiar with the internal composition of Venus, but I would guess that there’s internal energy from the decay of radioactive elements like 40K. However, the contribution to the surface temperature of this internal energy is likely to be on the same order as that for the Earth, i.e. insignificant

3. 33 degrees is an approximation so I would rather talk in terms of forcing. I’m going to use MODTRAN and as implemented it doesn’t integrate the full spectrum so the numbers won’t be the same as Kiehl and Trenberth, but will give you the idea. For clear sky conditions, 1976 standard atmosphere, 375 ppmv CO2, radiation from the surface is 360.472 W/m2 while radiation from the TOA (100 km) is 258.799 W/m2. So the total forcing is 101.673 W/m2. If we set CO2 to zero then TOA flux is 286.242 W/m2. That makes the CO2 forcing 27.443 W/m2 or 27%. It will be smaller as a percentage but larger in absolute magnitude in the tropics and larger as a percentage and smaller in absolute magnitude at high latitudes in winter.

4. The log decline means we have to look at log [CO2] and forcing rather than absolute concentration. We do that by talking in terms of doubling rather than ppmv. Going from 200 to 400 ppmv CO2 has about the same forcing as going from 400 to 800 ppmv.

5. I don’t understand the question.

6. Atmospheric radiation is controlled by the temperature and humidity profile of the atmosphere so it’s there day and night. The magnitude will vary somewhat with the temperature of the boundary layer and lower atmosphere.

7. I don’t think so. Cointegration and unit roots are useful to investigate the possible correlation of two time series where you don’t already know the physical (or economic) relationship. That’s not true for atmospheric radiative transfer. I’m reasonably certain that temperature is near unit root at best so conclusions based on temperature being identically unit root are flawed.

The question of climate sensitivity and models is whether the models provide useful projections of the variables used to calculate radiative transfer, cloud cover, precipitation, etc., not the radiative transfer itself. At least that’s my current thinking.

Don’t worry, nobody is challenging the basic laws of radiation, so you can dispense with the cheap shots about Nobels (and you wonder why I get angry discussing things with you?) The article in question merely challenges the MECHANISM of warming on the planetoids. Yes the surface of the water in Tahiti will radiate according to the forth power of the temperature and according to its emissivity. That, by itself, proves nothing however because it completely ignores heat storage effects.

The article in question is saying that you don’t need a greenhouse effect in order to explain why a planetoid is warmer than is predicted by the SB equations. That’s all. It isn’t trying to repeal any laws of physics. NASA found out that the moon doesn’t go back to 2.7K at night (AS WOULD BE PREDICTED BY CONSIDERING ONLY THE SB EQUATION), because it stores heat. And if that is true, how much of the observed warming is GHE and how much is due to stored energy?

The water surface near Tahiti is probably about 30 C at night. If I suspend a blackbody above that water,the water will radiate sufficient energy FROM THE ENERGY STORED IN THE WATER to warm the balckbody to 30 C. I don’t need any backradiation (and in fact such backradiation is problematic to me because then the temperature should maybe go even higher). That is not to say the radiation doesn’t exist; it simply does not control the temperature.

BTW, when Al Gore and Obama get Nobels, they just ain’t very precious anymore.

DeWitt; since CO2 collisional transfer only occurs with other CO2 then would not that process be exhausted by the formation of LTEs at the surface where CO2 absorption is maximum, with those LTEs transferred vertically to the characteristic emission layer [CEL] where the internal temperature of the LTE matches the surrounding temperature? It would also be the case that isotropic emission would be blocked by the opaqueness of the atmosphere underneath the CEL. If N2 and O2 do not get heated by collisional transfer from CO2 I presume you agree they are heated by conduction with the surface and insolation?

2 My comment about volcanic activity on Venus is based on an article by Craig O’Neill from Macquarie Uni in Australasian Science, Vol 29, April 2008. Apparently Venus has no plate tectonics which means the interior heat is released by episodic overturn which is also responsible for the gas composition and density of the atmosphere which traps the heat from the periodic episodes of crust overturn; sounds nasty and likely to generate more heat than Earth’s system.

3 yep, your estimate dovetails with Lindzen’s estimate that CO2 is responsible for about 8C of the 33C of the greenhouse effect, see page 3:

SOD: Another issue for you to consider posting about is just WHY none of the GHE effects of CO2 are being demonstrated. No “hot spot” in the upper troposphere in equatorial areas (as predicted by your hypotheses), no general heating of the planet (or oceans), no agreements between the famous GCMs and the real world. Nada. Without empirical evidence, you have nothing but theory in science. You have none so far. And the world is getting ever colder.

Apologies for my tone, I really thought you were claiming that 100 years of thermodynamics was all wrong because of a 2-page flyer.

-With that cleared up:

If you believe that the Stefan-Boltzmann and Planck equations are correct you are confusing 2 completely different effects.

On the earth we measure the temperature at the surface and calculate the average radiation of 396W/m^2 (which we verify, but anyway you are happy with the calculation).

This radiation is from an effective temperature of about 15’C. At the top of atmosphere we measure an effective temperature of about -18’C – this is the measured outgoing longwave radiation of 239W/m^2.

It appears you agree that both numbers are correct.

This is the “greenhouse” effect. See note at end.

On the moon “someone” possibly once thought that there was no heat capacity in the surface of the moon and so the surface would radiate out exactly what it received in at every point in time.

When this “someone” didn’t find this to be the case and when ilovemyco2 read about it, he got confused..

The fact that the surface doesn’t radiate out exactly what it receives in at every moment in time makes exactly like every other body in the universe (including the earth) and therefore my only surprise is that nasa “thought” differently (if that was the case).

In any case, this is the key point for the moon:

The radiation out from the surface averaged globally annually or fortnightly (or whatever the appropriate time period is) will be exactly what is absorbed by the surface.

(Unless the moon is slowly heating up or cooling down, in which case the absorption will be slightly more or slightly less than emission).

And, what is radiated into space from the moon will be exactly what is radiated from the surface which is exactly what is received by the surface of the moon. (All averaged as noted above)

The moon has no atmosphere so there is nothing to absorb the radiation between the surface and space. Unlike the earth.

But like the earth, the value of temperature and, therefore, emitted radiation at any one point on the surface at any one time will not be the same as the incident radiation on that surface. (Because real surfaces with heat capacities take some time to heat up and cool down).

This is not some mystery effect that demonstrates anything relating to the greenhouse effect.

I hope this makes sense.

Note:
Didn’t want to obscure the main points above. But the difference between the upward surface radiation and the upward top of atmosphere radiation is what needs an explanation. What happens to this radiation?

The moon doesn’t have this issue. The moon’s average emission of thermal radiation from its surface exactly matches what it receives from space. Unless the first law of thermodynamics is flawed.

But the earth’s average emission of thermal radiation from its surface doesn’t match what it receives from space at the top of atmosphere.

Another issue for you to consider posting about is just WHY none of the GHE effects of CO2 are being demonstrated. No “hot spot” in the upper troposphere in equatorial areas (as predicted by your hypotheses), no general heating of the planet (or oceans), no agreements between the famous GCMs and the real world. Nada. Without empirical evidence, you have nothing but theory in science. You have none so far. And the world is getting ever colder.

First of all it’s important to take the time to understand the basics.

If the only effect in climate was the “greenhouse” effect each passing year with a few ppm more CO2 should see an incremental rise in temperature. And a lack of that rise would falsify the “greenhouse” effect.

But climate is very complex and so predictions are more challenging. This would be the basis of Richard’s Lindzen’s or John Christy’s or Roy Spencer’s criticisms of GCMs and of the current “consensus”. But they all agree that the “greenhouse” effect exists.

Well, I’m not going to use the argument from authority because I don’t accept it myself. But still, if 1000’s who have studied a subject for decades all agree on something and I think they are wrong, it gives me pause for thought. It should give you pause for thought as well.

Whether the GCMs are right is a totally different subject than whether the “greenhouse” effect exists. The “greenhouse” effect is one component of GCMs. There are lots of other components, and many of them are more problematic than solving the radiative transfer equations.

“Well, I’m not going to use the argument from authority because I don’t accept it myself. But still, if 1000′s who have studied a subject for decades all agree on something and I think they are wrong, it gives me pause for thought. It should give you pause for thought as well.”

Sorry, but this kind of argument (argument from authority) simply holds NO WEIGHT in science. I’m surprised that you brought up this ridiculous argument.

“Apologies for my tone, I really thought you were claiming that 100 years of thermodynamics was all wrong because of a 2-page flyer.”

Thank you, apolgies accepted, of course. What I want you to consider is that the atmosphere, IIRC, “weighs” about 1,000,000 g/m^2 at the surface. With a heat capacity averaging about 1 joule/g/k, there is one hell of a lot of energy stored in the atmosphere. Do you not think this has ANY effect on the temperature/climate. How can you try to reduce everything down to a stupid little radiation diagram?

What I want you to consider is that the atmosphere, IIRC, “weighs” about 1,000,000 g/m^2 at the surface. With a heat capacity averaging about 1 joule/g/k, there is one hell of a lot of energy stored in the atmosphere. Do you not think this has ANY effect on the temperature/climate. How can you try to reduce everything down to a stupid little radiation diagram?

Everything is not reduced to a radiation diagram.

In fact, this article is about something completely different, but many people are still sure that the “greenhouse” effect doesn’t exist so we come back to the very basics again.

This radiation diagram is the point that needs explaining if you think the “greenhouse” theory is wrong.

It doesn’t matter how much the atmosphere weighs or how much heat it stores.

I must thank Science of Doom for his interesting articles.
In the section “Greenhouse Effect and Water Vapour”, he introduces an equation:

F = σTs^4 – G

I didn’t understand what this equation was trying to say. How are the Surface Radiation and the Outgoing Long Range Radiation linked, noting that there are other fluxes from the Surface into the Atmosphere? And one of these (evaporation) is stronger than the NET Surface radiation, while direct Conduction is also a significant flux?
The sentence “So the radiation from the earth’s surface less the “greenhouse” effect is the amount of radiation that escapes to space.” is not accurate.

Missing from this sentence are the following:
Incoming Solar Radiation Absorbed by the Atmosphere(A);
Evaporated Water from the Surface(E);
Direct Conduction from Surface to Atmosphere(C)
Back-Radiation from Atmosphere to Surface (B)

Writing down the fluxes for the atmosphere as a black box:
F= A+(S-B)+E+C (where S=Stephan-Boltzmann Surface Radiation),
Making G = S-F = B-A-E-C

So G doesn’t appear to me to make much PHYSICAL sense, and is certainly NOT the “Greenhouse Effect”, as the evaporative and conductive species are not greenhouse animals, but B and A certainly belong in the zoo.
It occurred to me that the equation may have arisen from the mistaken notion that it represents the behaviour of the planet with no atmosphere, and that as one adds atmosphere the G term appears. Unfortunately the planet is not a dry rock, so Solar Radiation – Reflected Solar Radiation = Outgoing Longwave Radiation is not correct for an Earth with no atmosphere.

I thought you’d mention the Fu/Spencer and Christy dispute about stratosphere temperature modeling! From your link is the accepted reason for stratosphere cooling:

“For carbon dioxide the main 15-um band is saturated over quite short distances. Hence the upwelling radiation reaching the lower stratosphere originates from the cold upper troposphere. When the CO2 concentration is increased, the increase in absorbed radiation is quite small and the effect of the increased emission dominates, leading to a cooling at all heights in the stratosphere.”

I don’t understand this; firstly, you can’t have stratospheric cooling without a THS; secondly, how can photons absorbed and then emitted by increased levels of CO2 produce a net cooling effect above what it would be if the CO2 wasn’t there; surely the effect on the CO2 molecule is temperature neutral and in the absence of collisional transfer the absorption/emission is a conduit? And if there is collisional transfer then the emission level would warm? If the increase level of CO2 takes the emission level into the lower statosphere how does the SB effect lead to a cooling?

A thought experiment. Put a kilogram of CO2 in a perfectly transparent spherical container and put that container in an evacuated cavity with perfectly reflective walls. If entropy were to increase every time a photon was emitted without an exactly equal decrease when a photon was absorbed (possibly the other way around), then the temperature of the gas would have to drop over time, yet there can be no loss in energy from the system by design. I think this violates the First Law. If no work is being done, then there is no change in entropy. I think this is related to the principle of microscopic reversibility. At the quantum level, the process looks exactly the same whether time is running forward or backward.

The concentration of CO2 in the stratosphere is low enough that a photon emitted upward is unlikely to be absorbed again. But collisional excitation still exists so IR radiation from CO2 and ozone results in an energy loss from the system. That loss is balanced by absorption of UV from the sun by oxygen and ozone and some absorption of IR from below. Since emission is a function of temperature, an increase in CO2, which does not change the absorption of UV and only absorbs a very small amount of upwelling IR, requires a reduction of temperature to maintain energy balance. The heat capacity of the stratosphere is low enough that the time constant for equilibration on the order of weeks to months rather than years. Petty has a more detailed explanation in A First Course in Atmospheric Radiation.

Well, let me backpedal a little here. I can identify with this diagram from NASA, since it seems to be a simple heat storage/release system:

I guess my explanation goes like this: The surface is heated each day by the Sun. Most of the IR released by the surface is absorbed by the IR-active gases in the air, mainly OCO and HOH (i.e., the “GHGs”). The energized GHGs heat up the air near the surface via collisions with the other molecules, notably N2 and O2 (thermalization) and by reirradiating to other GHG molecules. Because heated air rises, convective forces are generated, forming the spatial heat distribution that we call the lapse rate.

During the night, the GHGs near the TOA radiate to space which causes a few degrees cooling of the air column. Of course, some IR goes directly to space from the surface both day and night.

A lot of the heat is absorbed by water and other solids during the day, and these solids lose some of that heat at night, moderating the cooling of the air column at night.

After eons, a quaisi-equilibrium state has been reached, wherein about the same amount of heat is lost and gained by the planet each day.

Where I have difficulty is with diagrams such as K&T’s 1997 diagram, where backradiation complicates the system. I simply don’t see why the backradiation is needed to explain the system. NOW PLEASE HEAR ME (since few seem to): I know that the backradiation exists, since it is a fundamental property of the GHGs (I’ve identified chemical compounds using IR spectrometry!). I just wonder whether it has any effects on temperature, given the strength of the convective forces.

NOW PLEASE HEAR THIS, ALSO: I am NOT convinced that I’m correct on these ramblings. I’m a hopeless empiricist. I’m just a simple organic chemist, who is maybe spoiled by actually seeing clear proof for equations and theories. But I can find no empirical evidence for a greenhouse effect. On the other hand, the ilovemyCO2 article that I linked provides what seems to be some fairly solid empirical evidence that no greenhouse gas theory is needed to explain why the planets are warmer than they “should be,” based on simplistic SB approximations. That intrigues me, that’s all. I don’t give a damn who agrees or disagrees; I’m just trying to learn more, that’s all.

“On the other hand, the ilovemyCO2 article that I linked provides what seems to be some fairly solid empirical evidence that no greenhouse gas theory is needed to explain why the planets are warmer than they “should be,” based on simplistic SB approximations.”

The article doesn’t provide a mean surface temperature for the moon, so there’s nothing provided to compare to the SB blackbody moon.

“roughly 20° cooler than predicted by day and 60° warmer by night, the net result being a surface that is
40° warmer than predicted”

I am not convinced those figures can be averaged that way as if they are global.

Even if they can the predicted chart shows the day averages about 350K and the night averages 0K. So going by that graphic the predicted mean temperature over the entire day was 175K

So when they say “40° warmer than predicted” that implies a global surface temperature of the moon of 215K

Yet the moon is receiving about 295wm-2[1] sunlight. Run that through SB and a blackbody absorbing 295wm-2 should be 269K.

That means both the original prediction of 175K and the “40° warmer than predicted” are both significantly lower than blackbody. So their claim that the moon is warmer than SB claims is bogus by their own figures.

Few do, that’s why it doesn’t get discussed so much. But it was a climate model prediction from over 40 years ago regardless of how well anyone understands it. Models matching reality was the question.
And yes, stratospheric trends aren’t clear cut – as noted in the article – as measurement until recently has been limited.

“Thus (within the zone in question) the surface of the real moon is
roughly 20° cooler than predicted by day and 60° warmer by night, the net result being a surface that is
40° warmer than predicted.”

This is based on measurements at a single spot over he period of just a few months. No attempt is made anywhere in the “greenhouse moon” article or the cited reference to calculate a long term mean temperature of the Moon.

In the section “Greenhouse Effect and Water Vapour”, he introduces an equation:

F = σTs^4 – G

I didn’t understand what this equation was trying to say. How are the Surface Radiation and the Outgoing Long Range Radiation linked, noting that there are other fluxes from the Surface into the Atmosphere?

I think I understand the confusion.

If we needed to work out the temperature of the surface for example, we would need to net all of the various heat transfer components.

But all the equation above is saying, in essence, is that the upward surface flux less the “greenhouse” effect (G) is the amount of longwave radiation leaving the top of atmosphere.

This is just a definition of the parameter G. And this is a value/effect that we want to study

If we want to understand upward flux we only treat upward flux. Downward flux doesn’t cancel it out.

We are not considering solar radiation in this equation because by definition we are considering the longwave flux.

How can we just avoid stuff “by definition”? is your next question (assuming the first part made sense).

We are measuring longwave radiation with ERBE and trying to make sense of these longwave measurements – in conjunction with surface temperature and water vapor.

As we are measuring longwave we need the equations which deal with longwave. The reflected solar radiation needs to be excluded.

Does this answer the question?

Note: the chapter does have a more extensive explanation but there is still this kind of assumed knowledge, plus a mix of naming conventions for each parameter that makes it hard to follow.

Science_Of_Doom said:
“But all the equation above is saying, in essence, is that the upward surface flux less the “greenhouse” effect (G) is the amount of longwave radiation leaving the top of atmosphere.”

And that is precisely my (first) issue with the equation. The upward fluxes from the Surface are not confined to Radiation, but include evaporated water and direct conduction. The equation should therefore read:

F=S+E+C-G, instead of F=S-G

[where S=Stephan-Boltzmann Radiation from the Surface,
E = Evaporated Water from the Surface(E),
C = Direct Conduction from Surface to Atmosphere(C)]

As it stands, the equation G = S-F does not correctly define the Greenhouse effect.

If you read the article carefully, you will note that the author does not agree with the division of the TSI by 4, due to curvature. I don’t know whether this is correct, but it explains the discrepancy you note.

BTW, Chtu, it is my understanding that the “actual” temperatures shown in the diagram are measured values, not calculations. This indicates that the division by 4 (which is also done in predicting what Earth’s temperature “should be”) is not correct.

“If you read the article carefully, you will note that the author does not agree with the division of the TSI by 4, due to curvature. I don’t know whether this is correct, but it explains the discrepancy you note.”

No, it does not, since he hasn’t calculated the temperature curve him self. Cthulhu’s formula is not quite correct either. The curve was calculated using the combined radiation of Sun and Earth hitting the Moon and using the SB relationship which turns out to not give you an accurate short term temperature forecast.

“I know that the backradiation exists, since it is a fundamental property of the GHGs (I’ve identified chemical compounds using IR spectrometry!). I just wonder whether it has any effects on temperature, given the strength of the convective forces.”

This is my point: heat transfer by diffusion is, compared to heat transfer by convection, very slow; the greenhouse effect relies on collisional transfer of energy; 2 things about that; firstly, backradiation does not transfer heat; the isotropic stream of photons expressed in w/m2 simply allows the surface to reradiate more photons back into the atmosphere; secondly, since most of that reradiation is confronted with an already saturated surface layer of CO2 what happens to it? The vertical elevator of the dry and wet lapse rates has to be close to being adiabatic because the surface parcels of air, LTEs, are carried upwards without further emission from within to the CEL; downward air matches this process in energy terms.

“If no work is being done, then there is no change in entropy. I think this is related to the principle of microscopic reversibility”

Exactly, this is the contradiction; obviously in the atmosphere there is work being done; this was the point of the Constructal Law and MEP; what may be the case at the micro, theoretical level is confounded by the macro phenomenology.

“By definition, G is the radiation difference between the surface and TOA.”

Yeah. The surface is at 288 C and the “radiative TOA” is probably at about 230 C. So, naturally there will be a radiation difference! How is this a GHE? The difference simply reflects the difference in temperature which is due to the lapse rate!

To use the radiative-convective model to calculate how SURFACE TEMPERATURE will change, one needs to know how doubling CO2 will change the lapse rate. If the lapse rate changed 0.1 degC/km (2%) and the tropopause is about 14 km above the surface, the radiative-convective equilibrium theory would predict a surface temperature rise of -0.3 to 2.5 degK depending on which way the lapse rate changed. Without knowing how lapse rate changes, one can NEVER use radiative-convective equilibrium to predict surface temperature changes associated with GHG increases.

The problem with radiative-convective equilibrium is that everyone at some point choses to ignore the possibility of changes in lapse rate (convection) and pretends that radiative forcing tells the whole story for SURFACE temperature. The radiative-convective theory you have presented so far is only based on first principles of physics ONLY at high altitudes and an assumption – fixed lapse rate – that more sophisticated models (3D-GCM’s) suggest is wrong. These models suggest that the lapse rate will increase (from a less negative number), reducing the impact of your calculated 1.1 degC temperature increase at the tropopause.

Well the subject is a complex one.

In any decent coverage of the subject of temperature changes from CO2, there is a careful distinction between the results with tropospheric/surface feedbacks – and with.

Radiative forcing is defined as after stratospheric adjustment and before the much more complex and longer term surface/tropospheric increases.

And yes, everyone – as in climate scientists who write about it – do know and write about the fact that lapse rate and humidity will change. You can find 1000’s of papers on it.

Obviously that’s what much of the discussion is about in climate science.

“..The upward fluxes from the Surface are not confined to Radiation, but include evaporated water and direct conduction. The equation should therefore read:

F=S+E+C-G, instead of F=S-G

[where S=Stephan-Boltzmann Radiation from the Surface,
E = Evaporated Water from the Surface(E),
C = Direct Conduction from Surface to Atmosphere(C)]

As it stands, the equation G = S-F does not correctly define the Greenhouse effect.”

This equation – the original one in the article – balances radiation.

The radiation from the surface is only sigma x T^4.

Heat leaves by other means but the value of radiation is simply sigma x T^4.

Well, if we start adding convective heat to that number then subtract the outgoing longwave radiation – we will have a different parameter.

By definition, G is the radiation difference between the surface and TOA.}

Science of Doom has shifted his ground. The original claim was that G represents the “Greenhouse Effect” and that “the upward surface flux less the “greenhouse” effect (G) is the amount of longwave radiation leaving the top of atmosphere.”
I have shown that both those claims are incorrect. G does not represent the “Greenhouse” effect of an IR active atmosphere, as it contains terms (Evaporation and Conduction) which are plainly IR insensitive, nor does it represent the upward surface flux less the amount of longwave radiation leaving the planet.

What G represents is anyone’s guess, but it is not an easily identifiable physical quantity.

Hence my problem with the equation F=S-G as a starting point for any analysis – it doesn’t seem to represent anything coherent. Why not start with the TOA balance, the Surface balance, or the Atmospheric balance?

I am concerned about this. Is the whole theorem of climate sensitivity based on the incorrect notion that the factor G represents the Greenhouse Effect?

Note that the items at b are all converted to sensible heat, at various heights in the atmosphere, and are ALL then convected. For Conduction, we know this is at the bottom of the column. For Radiation, this is also very close to the ground, probably the majority of radiation is absorbed by 25m altitude (if you doubt this, check out the absorption tables for CO2). For Evaporated water vapour the injection of heat into the atmosphere is more spread out, and probably most of this heat enters the atmosphere literally in the clouds.

It is because the heat transport within the atmosphere is convective, regardless of how it leaves the surface, that I was so suprised at the strange equation
F= S-G being used as the starting point of sensitivity theory.

Note also the weedy influence of Surface Radiation on atmospheric heating. It amounts to only around one fifth of the Surface’s influence on the atmosphere. Again, I was suprised to see Surface Radiation as a star player in the equation under discussion.

I have to go with Colin on this. The greenhouse effect is the difference in the total heat leaving the surface and the total heat leaving the planet. The numbers don’t balance if you just look at radiation and don’t include sensible and latent heat (324 +168 in vs. 390 + 102 out). Absent convective heat loss, the average surface temperature would have to be 305K (492 W/m2) rather than 288K. That means the climate sensitivity is going to depend on how much evaporation/precipitation changes as a function of temperature as well as all those other less well known things like cloud cover.

Cohenite asked: “Colin; and of that 26w/m2 for net radiation how much is due to CO2?”

I cannot give an accurate reply – perhaps someone who has done the modelling of the lower atmosphere can help.
But in descriptive terms what is happening is this:
1. The Surface emits nearly Black Body radiation (390W/m^2 at 15DegC).
2. Most of this is absorbed by the Greenhouse Gases (320W/m^2) or reflected by clouds (30W/m^2, see the number given in Science_of_Doom’s piece above). The rest (40W/m^2) escapes to Space.
3. The amount absorbed is roughly in the proportion Water Vapour 2.5, CO2 1, Others not sure. So say around 220W/m^2 absorbed by Water Vapour, and 90W/m^2 absorbed by CO2.
4. This absorbed radiation is distributed through the immediately adjacent molecules as thermal energy (kinetic energy) by collision.
5. Greenhouse gas molecules which are involved in collisions will radiate energy, in the same frequency bands and with the same probabilities as they absorb radiation. Because they are colder than the Surface, the amount of energy radiated is slightly less than was absorbed.
6. The total “back radiation” is 324W/m^2, comprising 30W/m^2 reflected from clouds, and roughly 205W/m^2 from Water Vapour and 85W/m^2 from CO2, and say 5W/m^2 from other species.
7. So in NET terms, the radiation absorbed into the atmosphere is around 16W/m^2 by Water Vapour, 6W/m^2 by CO2 and 4W/m^2 by other gases.
8. There are a number of observations:
A. The above guestimates are really rubbery. Perhaps someone has much more accurate calculations.
B. The extent to which the window to space tightens with increased concentrations of CO2 and H2O is not known by me. Some spectroscopic experts consider that the CO2 and H2O bands are already saturated, ie that the addition of more gas doesn’t materially affect absorption, just the height of absorption, which is anyway mostly close to the ground.
C. If that is the effect of increasing concentration, we expect the net absorbed radiation to fall (back radiation to increase), as the temperature of the gases emitting the photons which reach the ground is higher, because they are closer to the Surface.

[…] It’s possible (although unlikely) that all the clouds would disappear and in which case the net incoming – reflected radiation might increase, perhaps to 287 W/m2. (This value is chosen by measuring the current climate’s solar reflection of clouds, see Clouds and Water Vapor). […]

This looks like good summary, but may I ask some questions from SoD or Colin… In point 5 you are talking about GH gas molecules, but what about other molecules – obviously most collisions must be between CO2 and N2 or O2. Looks like there must be some work done by collisions and some mechanical energy lost as entropy? Has anybody calculated how much?
Sorry, if this is dumb or dull question, but I have one more, even worse 🙂

Can we talk in the case of GHG-s about scattering of IR radiation instead of trapping the heat? Some part of IR radiation from the earth is converted to heat by collisions and some part of it scattered, right? We can’t see IR light, but if we could, wouldn’t it be similar to scattered blue light, when sky is blue? Only difference I see, is the fact that blue light is so much hotter than IR-light, tens of times, why don’t we have to worry about doom of blue catastrophy 😉 ?

In response to Allan Kiik, yes the majority of collisions are between non-GHG species. But every molecule in the atmosphere at ground level is colliding with a neighbour approximately 10^10 times per second. (These molecules are fairly whizzing about – the average velocity of a CO2 molecule is 400m/s.)
A photon of energy absorbed by a GHG molecule is converted into vibration of that molecule. This is an unstable situation, and left to its own devices the molecule would re-radiate the photon, with a half life around 10^-5 seconds. However, in the vast majority of cases a collision occurs before this can happen, and the energy is re-distributed as kinetic energy(sensible heat) between the two participants. This KE is then distributed through the whole ensemble by collision.
The net result is that absorbed radiation is converted to raised temperature of the atmosphere.
In accordance with the First Law, energy is not lost, just converted to another form (light becomes momentum).

On the other hand, while this is all going on, un-energised CO2 molecules are gaining vibrational energy by collisions, and in a very small proportion of cases, this will result in emission of a photon. So while some molecules are absorbing, some are doing the other thing…The rates of the processes are dependent on the species, the frequency of the photons, the temperature and density.

“The net result is that absorbed radiation is converted to raised temperature of the atmosphere.”

Do I understand correctly that radiation from ground heats air mainly in the first 25 meters? (I have seen other numbers too, Heinz Hug, for example, calculated it to be about 10 meters).
Does this mean also that all of the so called back-radiation must too come from 25 meters column?

I haven’t been ignoring your questions and comments, just trying to think about how best to respond.

Citing DeWitt Payne, but I think this also represents Colin Davidson’s point:

The greenhouse effect is the difference in the total heat leaving the surface and the total heat leaving the planet.

The balance of radiation at the top of atmosphere is something we agree on (?). As outgoing radiation at TOA is the only way that heat can leave the planet.

Regardless of convective and conductive fluxes, if the atmosphere absorbed and emitted no radiation, the surface radiation flux would be the same as the OLR at TOA.

So in a non-absorbing/emitting atmosphere G=0. This is with Ramanathan’s definition and everyone else appears to use it. Ramanathan defines G as the reduction in outgoing longwave radiation flux due to the presence of an absorbing atmosphere.

There is no problem with this “mathematical” identity. (?)

I think you are both questioning its usefulness – as in whether it relates to anything real in climate.

But if we want to work out the “heat retained” in the climate system (between the surface radiation (defined from the temperature) and the top of atmosphere) then we need to know G, and we want to find out how G is related to other parameters especially surface temperature via feedback processes of lapse rate changes and water vapor changes.

Perhaps it might seem like I am just saying the same thing as before.

Perhaps I am not very good at explaining this point that seems very clear to me.

(Trying again)..

With the definition that G is the difference between the measured TOA flux (F) and the surface radiation (=sigma.T^4), then if we can measure F and T we can find how G varies as a function of other parameters like water vapor. And we can find the relationship between Temperature (T) and G.

In radiative-convective models, convection is replaced by a fixed lapse rate which is magically maintained by whatever convective flux of energy (including latent heat) is needed to supplement radiative transfer. Lapse rate itself does not convey any information about rate of energy transfer, ie. how FAST energy is removed from the earth’s surface. Colin and Dewitt want to include values for convective energy transfer into these models, but they don’t really belong in this discussion because this model (as opposed to other types of energy flux models) automatically assumes these fluxes will change as the concentration of GHGs change.

This assumption leads to the absurd impression that convection is unimportant to AGW. Strangely, this is correct, BUT only at the tropopause where there is no temperature gradient to drive convection. This is one reason why radiative forcing is defined as the net change in radiative flux at the tropopause: There we can use changes in radiative forcing to make predictions about temperature change. The problem comes when Science of Doom and others try to tell us that the temperature rise at the surface will be the same as the temperature rise at the tropopause because the lapse rate doesn’t change. You can read more in my earlier comment (#2), which was accidentally posted as a reply to comment #1 and has never gotten a reply.

This assumption leads to the absurd impression that convection is unimportant to AGW.

Leads who?

The 1d radiative-convective model is an early step in solving the problem of climate response to CO2 and other trace gas changes.

The problem comes when Science of Doom and others try to tell us that the temperature rise at the surface will be the same as the temperature rise at the tropopause because the lapse rate doesn’t change.

At the moment, the top line of this post on Water Vapor and Clouds still says that a radiative forcing of 3.7 W/m^2 will produce a surface temperature rise of about 1 degC. When a specialist does this calculation for non-specialists and doesn’t explain that it applies to temperature change at the tropopause, this is a form of deception. When they don’t immediately add that our best estimate of changing lapse rate suggests that +1.0 degC at the tropopause will translate to only +0.4-0.5??? degC at the surface, the deception becomes worse. Nobody is reading this blog to understand climate change at the tropopause!

To be technically accurate, I should apologize for possibly implying that you said “the lapse rate doesn’t change”. However, the theory of radiative-convection equilibrium you described uses (requires?) a fixed lapse rate and, to my limited knowledge, you’ve never discussed whether it does change.

My interest in climate science started with my son asking questions about the table radiative forcing changes in AR4. The public is told to think of 1 W/m^2 as the warming produced by at network of 100W light bulbs spaced at 10 m intervals! The discussion near that table doesn’t provide the information needed to translate 3.7 W/m^2 into +1.1 degC at the tropopause and about +0.5 degC at the surface (without feedbacks). That understanding took hours of research to develop with satisfying confidence. (You still see plenty of people who cite 0.7 W/m^2, which comes from mistakenly adding 3.7 W/m^2 to surface emission rather than tropospheric emission.) Then I needed to wade through forcings that are reported in terms of W/m^2/degK, but which could easily be expressed more clearly. I’m extremely angry that the IPCC has deliberately made it difficult for the public to understand that the surface warming DIRECTLY due to 2X CO2 is predicted to be only 0.5 degK (the only area where the “science is settled”, probably). I get angry and make mis-statements when Science of Doom appears to do the same.

(I need to put my anger aside and focus on the quality of the evidence you present about water-vapor feedback. That’s what I’m here to learn about and that is tough slogging.)

At the moment, the top line of this post on Water Vapor and Clouds still says that a radiative forcing of 3.7 W/m^2 will produce a surface temperature rise of about 1 degC. When a specialist does this calculation for non-specialists and doesn’t explain that it applies to temperature change at the tropopause, this is a form of deception. When they don’t immediately add that our best estimate of changing lapse rate suggests that +1.0 degC at the tropopause will translate to only +0.4-0.5??? degC at the surface, the deception becomes worse. Nobody is reading this blog to understand climate change at the tropopause!

The solution to the radiative transfer equations to calculate “radiative forcing” produce a +1.2’C temperature rise at the surface prior to any feedbacks. (Strictly speaking, this is after stratospheric adjustment – which is a feedback).

Allan Kiik asked (0824, 6JUN):
“Do I understand correctly that radiation from ground heats air mainly in the first 25 meters? (I have seen other numbers too, Heinz Hug, for example, calculated it to be about 10 meters).
Does this mean also that all of the so called back-radiation must too come from 25 meters column?”

I may have overstated the case.
In the case of CO2, the figures for Wavenumber 650 (not the strongest absorbing frequency, which is 670, but i don’t have numbers for this) are over 50% absorbed in the first 25m, and over 92% in the first 250m. John Nicol (see http://www.middlebury.net/nicol-08 ) calculates almost complete absorption in the first 5m for Wavenumber 670. So in the case of CO2, probably the majority of absorption is within the first 25m, with near extinction by 250m.

I don’t have any figures for H2O absorption. I suspect that it is weaker, but likely that most absorption occurs below 500m.

And yes, that means that the back-radiation must be coming from low down – otherwise it gets absorbed by the under-lying gas before it gets to the surface.

Incidentally, Nicol’s paper is well worth a read. It is somewhat mathematical, but the spectroscopic/emission science is main-stream and uncontroversial. I think his calculation of the temperature effects at the surface is flawed (he omits back-radiation and evaporation), but the rest looks pretty much correct.

There are a number of issues I have with the equation used by Everyone.

1. It does not represent the Greenhouse Effect.
2. It leads to incorrect values for sensitivity and feedback.

The first point is undeniable. If there were no atmosphere there would be no conduction. But the conduction term is solely dependant on the presence of an atmosphere, not of GHGFs within that atmosphere. The case of evaporation is even stronger. This will occur whether or not there is an atmosphere. In this case the presence of an atmosphere INHIBITS this major flux from the surface. (evaporation would be much stronger if the vapour pressure =0). The rate of evaporation is not dependent on the Greenhouse.

Evaporation is not a “feedback”. It is very like the Stephan-Boltzmann radiation – as soon as the temperature changes, so does the evaporation rate. Lumping Evaporation in with the “Greenhouse Factor” is just plain silly, and leads to a wholly incorrect value for the base sensitivity of the Surface.

I have shown that the Surface sensitivity lies between 0.095 and 0.15DegC/W/m^2, and have not seen any convincing counter argument. This is a fair way different from tho 0.25 people calculate using the Stephan-Boltzmann relation on its own, a calculation I regard as completely flawed, as it ignores the MAJOR flux from the surface into the atmosphere.

I agree with Frank. A Radiative imbalance at the Tropopause does not mean an imbalance at the Surface. There is no way for such an imbalance to be communicated to the Surface, unless one believes in a magical flow of energy from the cold Tropopause to the hot Surface down the immobile snake of the immutable lapse rate. If there is a radiative imbalance at the Tropopause, that portion of the atmosphere will heat up until the imbalance is rectified. Full Stop.

Colin: Frank thinks that a warmer tropopause will reduce the rate at which convection transfers energy from the surface to the upper atmosphere (where it can more easily escape by radiation mostly because there is much less water vapor left to pass through). This will eventually warm the surface (though I might not call it an “imbalance that warms the surface”). I’m hoping that Science of Doom will soon discuss the physics that controls the lapse rate – which is where convection and latent heat enter the picture. Unfortunately they don’t appear in the form of an energy flux – which is innately confusing to me.

Colin: When a packet of warm air rises, it expands (due to the lower pressure) and therefore cools. (If cooling causes condensation, release of latent heat reduces the temperature drop.) If it is now cooler (and therefore denser) than the air immediately above, it won’t continue to rise. For that packet of air to keep rising, the rate of temperature decrease with altitude needs to be greater than the temperature decrease due to expansion. So heat should flow upwards when there is a steep temperature gradient with altitude and stop flowing when the gradient has been reduced. Radiative forcing at the tropopause will produce a small decrease (1-2%) in the gradient, presumably stopping convection in locations where the driving force was marginal.

However, you are completely correct that the atmosphere is not in an equilibrium state with the same lapse rate everywhere. The sun shines only half of the time. When it is shining, the air near the surface, particularly over land, heats up enough exceed the maximum gradient for stability; and packets of warm air being to rise in some places and to descend in others. A complete cycle from near the surface to the tropopause and back apparently takes several weeks. It may be dangerous to apply equilibrium considerations to a system that is far from equilibrium because of the massive shift between day and night (and sunshine and overcast) in a system that apparently takes weeks to respond.

I looked a two radiosonde sites. Both had fairly straight line changes in temperature with altitude at -6.5 and -5.8 degK/km. The former was in the tropics and supposedly had a large amount of potential convective energy, which would be sensible if the humidity were high. The latter didn’t.

ie the change in “Earthlight” is the same as the change in OLR. As one goes up, the other goes down by exactly the same amount (assuming an equilibrium state, which is implicit in all this discussion.)

So one can measure dF directly by measuring Earthlight.

A second implication is that if there is no change in planetary albedo, then F is a constant, and dF/dT is zero.

E is included in G in the case of an atmosphere, but “in a non-absorbing/emitting atmosphere G=0.”

I think the quoted phrase is incorrect, or, probably, that in the case of a non-absorbing/emitting atmosphere E=-C, ie the atmosphere heats up due to the Evaporation flux, and this atmosphere balances by conduction to the surface so that the temperature of the Surface is permanently less than the temperature of the air immediately above the surface. ie Ts is not the air temperature, but some lower temperature.

Do I understand correctly that radiation from ground heats air mainly in the first 25 meters? (I have seen other numbers too, Heinz Hug, for example, calculated it to be about 10 meters).
Does this mean also that all of the so called back-radiation must too come from 25 meters column

I’m sure this is wrong. When I find the source (which was a textbook or a published paper) I’ll post it here. The “average height” for the backradiation was in the upper troposphere. That doesn’t mean the peak lines of CO2, water vapor, CH4 aren’t very close to the ground.

If you find your source that provides the 25m or 10m number please post it.

There is no way a CO2 photon from the Upper Troposphere (10km) will make it past all the CO2 molecules to the ground.

For wavenumber 650, these are the transmission figures:
Concentration, atmcm: 0.2/0.5/1/5/10/100/1000
Transmission,%: 74/61/48/16/8/0.1/0

1 atmcm is the same as 25m of atmosphere at STP. So if a wavenumber 650 photon originates from 25m up, it only has a 48% chance of making it to the surface. From 250m the chance is 8%.

The strongest CO2 emission/absorption is at wavenumber 670. I don’t have figures for that, but it is clear that a 670 wavenumber photon will be extinguished by a lesser depth of atmosphere.

The 50% points for wavenumbers 600 and 700 are about 500m and 75m respectively.

These are the low power edges of the CO2 emission band. It is clear that for CO2 at least, the majority of the back-radiation is mostly coming from very low in the atmosphere.

There is another consideration. Emission lines from a higher place (a lower temperature and air pressure) are much less broad than from low down. So there is very little power in the wings of the lines, and emission is concentrated into the strongest parts of the absorption lines of the gas in the lower atmosphere. From this point of view, the CO2 emissions will be more quickly extinguished than the tables indicate.

I don’t have any figures for water vapour absorption. But given this gas is generally in very high concentrations compared to CO2 I would be suprised if the picture was very different.

I will try to get to the local public library this week to hunt down the relevant figures.

Based on my naive appreciation of the physics of the processes I tend to agree.

Assuming a relatively short mean free path – gas density dependent, then radiative energy transfer will tend to flow down the density gradient. That is, energy in denser gas locations will tend to flow towards less dense locations simply because it’s easier to do so – it gets further with each emission in the direction of lower density.

This is the naive assumption. I am sure there are more factors involved such as gas temperature and chemical make-up.

Using this naive assumption, then energy from very high up is very unlikely to *net* transfer to lower layers. There is no reason that *some* energy can’t be transferred downwards, but the net radiative energy transfer will always be from higher density to lower density

Both papers are from time 10-12 years ago, so they can be somewhat outdated, but both are based on lab measurements and I guess there is still some value, even if the results can be explained differently.

“I am talking about the “average” from the atmosphere, which includes, for example, 8-12um. What are the transmission % in these wavelengths? The atmosphere is almost transparent at these wavelengths.”

That is an interesting turn – as “transparent” means relative absence of absorbers/emitters then who will radiate in this band (at nighttime)?

A few points about Back Radiation.
1. Gases which are good absorbers will be good radiators. Radiation occurs at the same frequencies and with the same line wings as the particular molecule absorbs.
2. The lower the level of emission the stronger the emission (higher temperature, higher no of molecules/cu mtr) and the wider the wings (Collision bandwidth is dependant on temperature and pressure)
3. IR inactive gases do not participate.
4. The two main GHGs are Water Vapour and CO2.
5. In the main CO2 emission bands we have established that the height of emission of the back radiation is close to the ground. [Who cares about the weedy emissions from weak bands? There’s little power there.]
6. 50% of water vapour is below 2000m. Even if absorption is not a factor(which it most assuredly is), most of the back radiation is therefore coming from below 2000m. [Again, who cares about the low power from weak bands?]
7. In summary, the majority of the Back Radiation power is provided by the two major GHGs. It has been shown that in both cases, the majority of the power is coming from 2000m and below. The claim that back radiation is coming from the high Troposphere is, on the face of it, unsustainable.
8. The reverse argument applies to absorption of Surface Radiation by the GHGs. In this case more than half the absorption (and conversion to convective heat) is complete by 2000m ( I will refine this estimate, which is an upper limit, when I dig out the water vapour absorption figures).

On the effective radiating height of “back-radiation” – I will use your figures for now because I cannot find the data I saw recently. Perhaps I was dreaming. I don’t think it is particularly important for the subjects we are discussing, although like many climate “facts”, quite interesting.

On your comments on the equation for “greenhouse” effect and feedback, I will give the matter some thought and post further comments, or a new post.

Thank you for your reply. It looks like I owe you another apology. Changes in lapse rate technically are feedbacks. Next, I suppose lapse rate feedback will be combined with water vapor feedback (which is useful in some situations) and disappear. Very deceptive. How about a little more candor? “The calculated temperature rise for a forcing of 3.7 W/m^2 (defined at the tropopause) due to 2X CO2 produces a temperature rise of 1 degK at the tropopause. What does this tell us about temperature change at the surface? Before we can say that 2X CO2 will produce the same 1 degK rise at the surface, we need to know that the lapse rate hasn’t changed, and a tiny change in the lapse rate (-6.7 degK/km) can have a significant impact on how temperature change at the tropopause translates to the surface 10 km or more below. In practice, lapse rate is expected to change, reducing the temperature rise at the surface by about 0.5 degK. However, the same factors that change the lapse rate (feedbacks) are expected to enhance warming at the tropopause – before lapse rate is used to project changes at the tropopause onto the surface. Since feedbacks can amplify and cancel each other, it is mathematically dangerous to separate lapse rate feedback from other feedbacks. Therefore, it is technically accurate, albeit confusing, to say that 2X CO2 will produce a 1 degK increase in surface temperature BEFORE FEEDBACKS, even though the calculation is formally correct only at the tropopause.”

Congratulations on your excellent blog. Very informative.
Water vapour feedback is an important and complex issue, so I was particularly appreciative of this post. Thanks also for the link to the “The Radiative Forcing due to Clouds and Water Vapor” chapter by Ramanathan et al in the 2006 book, which I have read with interest.

However, I take issue with your statement “It should be clear from these graphics that observed variations in the normalized “greenhouse” effect are largely due to changes in water vapor.” The spatial maps referred to merely indicate a correlation between these two things. It is unscientific to infer causation from correlation. Ramathan himself goes no further than to say the graphics suggest that variations in water vapour rather than lapse rates contribute to regional variations in the greenhouse effect.

I think, in common with various other repondants, that changes in lapse rates and in the height of the tropopause are key issues in modelling the greenhouse effect, yet they seem rarely discussed. Ramanathan’s chapter does not really cover them.

With water vapour and CO2 being such strong absorbers, it would not be surprising if the transmission of heat from the surface to the upper troposphere were dominated by convection, with very little from radiant energy in the bands absorbed by water vapour and CO2. In that case, would one not expect further increases in those gases in the lower and mid troposphere to have little effect except insofar as they change the lapse rate and/or the height of the tropopause?

“7. In summary, the majority of the Back Radiation power is provided by the two major GHGs. It has been shown that in both cases, the majority of the power is coming from 2000m and below. The claim that back radiation is coming from the high Troposphere is, on the face of it, unsustainable.”

True but not complete. Suppose we assume that all the radiation from the surface is absorbed in the first kilometer. Then what? The top of that 1 km layer also emits radiation upward, in fact, if we slice the layers thin enough, each layer emits the same amount of radiation upwards as downwards. If each layer doesn’t receive radiation from the layer above, it must cool until the energy in and out balance. But of course, each layer does receive radiant energy from the layer above. But because there’s a temperature gradient in the atmosphere, each layer receives a little more energy from below than it does from above. Convective transfer from the surface complicates the calculation, but doesn’t invalidate the point. In fact, the main function of convective transfer is to define the temperature gradient.

So the radiation from the bottom of the atmosphere does depend on the radiation from higher in the atmosphere, all the way to the stratosphere, in fact.

If the back-radiation is coming from the first kilometre of atmosphere, it means that the net radiative flux from the surface into the atmosphere(surface_radiation – surface_radiation_escaping_to_space – back_radiation) is thermalised within that first km.

So all the fluxes from the surface are thermalised and become convective fluxes within the atmosphere. These are, in INCREASING height of entry into the atmosphere:
a. Conduction, 24W/m^2 at the surface.
b. Radiation, 26W/m^2 in the first km.
c. Condensation of water vapour into mist, clouds, fog, frost etc, mostly in the clouds, 78W/m^2.

I’m not sure about radiative transfer within the ensemble. Most authors state that heat transfer within the atmosphere is primarily by convection. But I can’t fault DeWitt Payne’s argument.

“So all the fluxes from the surface are thermalised and become convective fluxes within the atmosphere. These are, in INCREASING height of entry into the atmosphere:”

You have it exactly backwards. Convection is most important at the surface and becomes rapidly less important as a means of heat transfer within the atmosphere as altitude increases. Convection becomes insignificant at the tropopause.

Ramanathan’s evidence for a strong water-vapor feedback is not convincing. I hope Science of Doom will be adding better information.

1) Energy flows from the equator to the poles as well as from the surface to space. Within a band of latitudes, F = oT^4 – G – W, where W is the net energy exported to other latitudes. Therefore dG_clear/dT includes other factors besides water vapor and lapse-rate feedback. Without evidence that longitudinal transport of energy is negligible, readers should ignore data for individual bands of latitudes.

2) The feedback data could have been cherry-picked. Other figures show ERBE data for 1985-1989, but dG_clear/dTs was calculated using data from only one year. Ramanathan says (p141): “The period 1985–87 was marked by ENSO, which peaked with the El-Nino event in 1987. Since the annual-cycle signals were weak during this ENSO, we employ only the years 1988–89 for the correlation analysis here.” What kind of excuse is this? Water-vapor feedback doesn’t change during El Nino. El Nino didn’t last for all but one year of the 1985-89 period. When the annual temperature cycle is weak, we have the opportunity to observe how much OLR (including instrumental noise) varies NATURALLY – without being driven by changes in Ts. If G_clear varied by only +/-0.5 W/m^2 when Ts was relatively flat, then the tight correlation in Figure 5.12 is meaningful. If G_clear varied by +/-5.0 W/m^2 without surface change, then the tight correlation is grossly misleading. On p145, Ramanathan tells us that the uncertainty in ERBE is “about 5.0 W/m^2 for time and spacial mean values”.

3) Since Ramanathan’s analysis of water-vapor feedback was published, we have accumulated more than two decades of improving OLR data and Ts data. Problems with ERBE data have been uncovered and better instruments have entered operation (p145). Neither Ramanathan’s (non-peer-reviewed?) 2006 book chapter nor Science of Doom tells anything about G_clear/dTs for any period besides 1988-9. Why? (If this approach to the most important feedback has been abandoned for the past two decades, scientists must no longer believe in it.)

DeWitt Payne (2010 10JUN) said:
““So all the fluxes from the surface are thermalised and become convective fluxes within the atmosphere. These are, in INCREASING height of entry into the atmosphere:”

You have it exactly backwards. Convection is most important at the surface and becomes rapidly less important as a means of heat transfer within the atmosphere as altitude increases. Convection becomes insignificant at the tropopause.”

I agree with the last sentence, except in the case of tropical thunderstorms.

The surface radiative flux(26W/m^2) enters the atmosphere as sensible heat, and the conductive flux(24W/m^2) and condensation of water vapour(78W/m^2) enter the atmosphere as sensible heat, as does the solar flux (67W/m^2) [All figures are from Kiehl & Trenberth 1997, which is repeated in IPCC AR4, WG1, Chapter 1].

These fluxes enter the atmosphere at varying levels. Conduction at ground level, surface radiation in the first km, condensation from the ground to the clouds, solar radiation mostly in the stratosphere.

The outgoing long-wave radiative(OLR) flux leaving the atmosphere is comprised of:
1.Surface radiation not trapped by the greenhouse (40W/m^2 which seems far too low to me…)
2. Radiation from the tops of the clouds and from the “top” of the water vapour. I’m not sure exactly where this is, but this is the main source of OLR, and is likely coming from around 4km. Shall we guess and say around 140W/m^2 (using Science_of_Doom’s ratio of 2.5:1 for the relative efficacy of Water Vapour and CO2)?
3. Emissions from other GHGs (mostly CO2?), from a thinner higher and colder place. Shall we say the remaining 55W/m^2?

So DeWitt Payne’s statement: ” Convection is most important at the surface and becomes rapidly less important as a means of heat transfer within the atmosphere as altitude increases.” is sort of right. There is very little upward heat transfer going on above the clouds to the GHG (less water) emission area. Most of the energy for that is coming direct from the sun. The rest is likely convected up by thunderheads.

“1.Surface radiation not trapped by the greenhouse (40W/m^2 which seems far too low to me…)”

Radiation directly to space under clear sky conditions is about 90-100 W/m2 on average. Using the MODTRAN 1976 standard atmosphere conditions, the surface radiates 360.472 W/m2 over the spectral range from 100 to 1500 cm-1. The calculated average transmittance at 100 km looking down is 0.2527 so the transmitted flux is 91.1 W/m2. But add cloud cover and the transmittance is zero. All surface radiation in the thermal range is absorbed by clouds. So if cloud cover is about 60%, then only 40% of the 90 W/m2, 36 W/m2) emitted from the surface escapes directly to space.

Clouds have an emissivity/absorptivity in the thermal IR pretty close to 1 so cloud tops effectively form a new surface that can emit to space. There’s less atmosphere above them so the transmittance directly to space is higher. But the cloud tops are colder than the surface below them so they emit less. The higher the cloud top, the colder the temperature and the less emission. K&T calculate that emission from cloud tops directly to space averaged over all types of clouds is about 30 W/m2.

The treatment of clouds is one of the places where I think Miskolczi’s model breaks down because it’s too simple.

1. F= Sunlight – Reflected sunlight. Unless the earth’s short-wave albedo changes, the Outgoing Long-Wave Radiation(F) is constant, whatever the state of the Greenhouse. So dF/dTs does not represent the Greenhouse Effect, but is a representation of the change of surface temperature with cloudiness.

2. F= S(urface Radiation) + G, but G= E(vaporation) +C(onduction) + A(bsorbed Solar Radiation) – B(ack Radiation). Of these terms, only A and B are Greenhouse dependent. C and E are Greenhouse independent. dG/dTs is therefore not a measure of the Greenhouse Effect.

3. It is unclear if the amount of radiation from the surface escaping “through the window” direct to space is constant. If CO2 concentration increases we expect some tightening of the window, but not much. On the other hand any increase in surface temperature will increase the amount of radiation, so the two processes may balance. Kiehl and Trenberth keep this constant at 40W/m^2 despite raising the surface temperature over time by 1DegC, suggesting that it may be close to constant.

Assuming that is so, the fluxes warming the atmosphere from the Surface are constant, the (B)ack radiation increasing by roughly the same as the sum of the increases in Radiation from the Surface(S) and (E)vaporation. Basically when the surface temperature increases, the increase in Evaporation is balanced by a
decrease in Net Surface Radiation Absorbed by the Atmosphere.
As the heat entering the lower atmosphere is unchanged (though the amounts entering at each height will change), the overall Lapse Rate to the tropopause will be unchanged. So the temperature at the Tropopause will always be the Surface Temperature minus a Constant. The sensitivity of the Tropopause temperature is therefore the same as (and driven by) the sensitivity of the Surface temperature to changes in “forcing” (either solar or back-radiation).

I hope this question is appropriate in this section as it is about water vapor.

If fossil fuel is burned, you get both CO2 and H2O. For instance, burn a benzene molecule (C6H6) and you get 6 CO2 molecules and 3 H2O molecules. The CO2 molecules will increase the Earth’s temperature, CO2 being a greenhouse gas. But H20 is also a greenhouse gas, a much better one than CO2. So why is the H2O that comes from burning fossil fuel not responsible for a part of the measured warming?

If fossil fuel is burned, you get both CO2 and H2O. For instance, burn a benzene molecule (C6H6) and you get 6 CO2 molecules and 3 H2O molecules. The CO2 molecules will increase the Earth’s temperature, CO2 being a greenhouse gas. But H20 is also a greenhouse gas, a much better one than CO2. So why is the H2O that comes from burning fossil fuel not responsible for a part of the measured warming?

That’s a good question. The reason is that there is a massive supply of potential water vapor – the oceans and waterways of the world – and the limiting factor is the ability of the air to hold it.

If – for example – all the water vapor was magically removed from the air overnight, within a few months the air would have as much water vapor as before.

That’s not the complete story because there are anthropogenic sources of water vapor which keep areas humid that wouldn’t have been humid before – thus changing the climate. From memory, this is mainly agriculture (irrigation) in Asia and the IPCC AR4 (2007) has a section on it.

1) if water vapor is such an important positive feedback (most of the alleged temperature rise is due to the extra water vapor and not the CO2 itself), then adding the stuff directly should have some impact. If it becomes more cloudy then temperature will rise and the air will hold more water, just as with an increase of CO2.

Alternatively, that fossil fuel water vapor could also be turned into the kind of clouds that are a negative feedback.

2) if people will start burning H2 instead of fossil fuel, we still put a lot of water into the atmosphere.

The subject of water vapor is a difficult one. In one sense you are right.

But if there was no shortage of water vapor, only the ability of the atmosphere to hold it, then producing more water vapor wouldn’t change anything. It would condense back to water and end up on the surface of the earth. The climate is more complex than this, but at a simple level this is probably the best way to think about it.

One answer to the question of why Ramanathan’s method has not been been used as new data has become available. Ascending branch – skies are cloudy; Descending branch – skies are clear

Roy W. Spencer, Ph. D. says:
September 16, 2010 at 9:37 AM
Frank-
Raval and Ramanathan’s 1989 paper was long ago criticized for the mistaken assumption that water vapor feedback can be inferred from the difference between the ascending and descending branches of atmospheric circulation systems. It cannot.

Feedback must instead be evaluated as the area- average response of the entire circulation system to a temperature change. I know of no one who accepts that the R&R89 paper demonstrates positive water vapor feedback…(although I’m sure there must be a few).
-Roy

[…] have a huge impact on the radiative (and convective) heat transfers in the atmosphere. From Clouds and Water Vapor – Part One: Clouds reflect solar radiation by 48 W/m² but reduce the outgoing longwave radiation (OLR) by 30 […]

They argue that rapid transpiration and subsequent condensation from coastal forests can create a pressure gradient that sucks in (pumps in) moist ocean air, feeding moisture recycling into the deep interior of continents. Seems to be a modern twist to the old adage that “The rain follows the plow,” i.e. forests create rain, and not the other way around.

The debate around the proposed mechanism revolves around basics of atmospheric physics. I’d be interested to hear what you think about this.

Makarieva’s biotic pump is based on her mistaken hypothesis that condensation causes a drop in pressure in the atmosphere. Her hurricane paper based on this idea was discussed at great length at The Air Vent (http://noconsensus.wordpress.com/)and The Blackboard (http://rankexploits.com/musings/). Go to The Blackboard and search on Makarieva. There are too many threads to list here.

The Air Vent doesn’t have a search function, but if you do a search on ‘Makarieva The Air Vent Hurricane’ the posts there should be listed.

[…] the limitation to absolute humidity at a given temperature for saturated air. Science of Doomcovers this rather well. Pointing out that water vapor is Earth’s dominant greenhouse gas does not minimize […]

If you go to Google Scholar and paste in the title of any paper, it will direct you to the original source and to any non-paywalled copy of the paper that is accessible. As a bonus, if the paper you want to see is only behind a paywall, you get a list of related papers and information about which ones are not behind paywalls, including newer papers that cite the full title of the paper you wanted. There are other ways to find papers with Google Scholar, but searching for the full title works best for me (and I often copy titles directly from the journal’s website).

Pekka –
I have been looking at Fig. 9.1 in Pierrehumbert’s text, which shows (using 1987 CERES data) that the net top-of-atmosphere radiation imbalance (averaged over a year) is hemispherically symmetric. The paper by Stevens and Schwartz shows that the net reflected radiation (and, of course, the average albedo) is likewise symmetric. This of course implies that net absorption of solar radiation is symmetric. I wonder if there is an update to the 1987 CERES data (via ERBE) that might show just how tight the symmetry really is. This is an extraordinary observation. It would be of interest to see the month-by-month variations.
I’d still like to know your views on https://scienceofdoom.com/2010/05/30/clouds-and-water-vapor-part-one/

I’m not ready either to make any strong comments on this post of SoD or on the paper of Ramanathan and Inamdar. One thing to notice is that the paper is not from the year 2006, when the book was published, but finalized probably in 2000 and based mostly on data available already a few years earlier. Two references from 2000 are given, but not really used, and almost the same applies also to papers from 1999 and 1998 (except perhaps for one paper of their own written in 1997).

Pekka: If you ever do chose to look critically at this work (particularly the awesome fit between Ga and Ts in Figure 5.12), I’d sure appreciate any comments on whether this is a general result or a chance occurrence during one year of more than 30 years of satellite observation of the earth. I once looked, but could find no one else who had obtained such strong evidence of clear-sky water vapor feedback using this method. This review article cites no supporting work done in the decade between the initial publication and this review article.

All papers that discuss monthly data seem to contain a statement warning that monthly data is not necessarily representative of warming on longer time scale. The paper referred above formulates that:

One can argue whether the strength of the feedback inferred from the annual variation is relevant to global warming. Nevertheless, it can provide a powerful constraint against which every climate model should be validated.

Similar comments are given also in IPCC WG1 reports when referring to these results. (The Tsushima and Manabe paper is not mentioned in AR5, it missed the deadline.)

Pekka: Thanks for the paper. I’ve wondered ever since SOD made this post how definite the work was. An analysis based on a single year was meaningless and each year might give a different answer.

It should be noted that the twelve data points (one for each month) on these lines is the average of the mean global temperature for that month and the average outward LWR and SWR for that month. So they have “hidden” a significant amount of the variability in the relationship between temperature and radiative cooling in these plots and probably inappropriately reduced the confidence interval for their calculated gain factors.

If I understand the paper correctly, about half of the gain occurs in the SWR channel. More SWR is reflected to space during during winter in the NH when the whole globe is colder. This may be due to albedo changes from snow cover and the increased intensity of incoming SWR (from our elliptical orbit). It certainly has nothing to do with the fast feedbacks from water vapor and lapse rate. The difference between clear- and all-sky is varies little with the annual cycle, so it isn’t cloud feedback either. Furthermore, the data in the SWR channel is fairly noisy and the uncertainty in the SWR slopes must be large. I think SOD’s post on R&I’w work is only on LWR feedbacks. It isn’t obvious that the earlier work was confirmed or not. Most climate models over-estimate feedback in the LWR channel.

I’m not particularly worried about the cause of temperature change (annual cycle, volcano, or CO2). It seems to me that – to a first approximation – that the feedbacks that effect radiative balance will be the same no matter what causes the temperature to change.

I’d prefer that they focus their analysis on lamba and not break it down into lamba_0 and lamba_f, followed by reporting g, the ratio of these two. I’m not convinced we know lamba_0 perfectly, that number is derived from models. Errors propagate unnecessarily from this point. What happens to the planet depends on lamba.

Pekka: Correction to my November 11, 2013 at 8:47 am comment. The outgoing SWR was normalized to incoming solar radiation to remove the influence of the annual cycle in solar irradiation from the analysis of feedback. This appears to leave the increased albedo due to snow cover in the NH winter as the primary reason more SWR is reflected when the globe is colder in clear skies. And about half of the total gain comes from the SWR channel. I’m not sure the same feedback in the SWR channel will occur following forcing by GHGs rather than the annual cycle.

I was more interested in the fast feedbacks that are found in the LWR channel. The middle of page 7569 left hand column says “The gain factor of the longwave feedback for all sky obtained here is 0.28 and is similar to 0.32 (i.e., that of clear-sky feedback), yielding −0.04 as the gain factor of longwave CRF.” The long wavelength channel presumably contains the gain due to the combined water vapor-lapse rate feedback in clear skies and it is not big enough to double the no-feedbacks climate sensitivity. At the moment, I am having trouble understanding the difference between these papers can converting the answers to terms I understand (climate sensitivity).

I’m becoming less enamored with the annual cycle. When the earth is closest to the sun, the solar forcing results a reduction in mean global temperature because the heat capacity of the NH is smaller than the SH. Clearly this isn’t an equilibrium response. The fast feedbacks (water vapor, lapse rate and clouds) respond quickly enough to this non-equilibirum temperature change as does annual fluctuations in albedo do to changing snow cover (which usually disappear when working with temperature anomalies.)

The analysis of SW is influenced strongly by several factors, which may contribute also to the differences between models.

The clear sky albedo is affected most strongly by the type of surface of the clear sky regions, and in particular in the clear sky regions of highest insolation. Snow covered regions have the highest albedo, but the albedo of desert areas is also well above average. Monthly graphics of the albedo for both cloudy and clear sky can be found from this link. The Antarctic would contribute much to that, if it were not cut off by a latitude restriction. The northern regions have a lower incoming flux during the winter and should therefore have a smaller weight, but it’s not clear, how that point is handled.

Tsushima and Manabe exclude latitudes higher than 60 and by that much of the snow cover. I don’t understand the argument they present for the exclusion as regions with no sunshine contribute zero to the reflected radiation. The argument seems to imply that they divide by the incoming flux of each latitude in the calculation, but that makes calculation of the global reflected flux almost meaningless. It would make more sense to divide by the global incoming flux that varies only because of the eccentricity of the Earth orbit.

Interpreting the SW results is difficult for the above regions. The results are also much less convincing as they show more variability than the error bars allow (that might be due to a difference between spring and autumn, but the paper does not show the data needed to see whether that’s the case).

The 1997 paper of Cess et al contains an interesting Figure 1, which shows how similar the data of four years are for the January, but unfortunately only for January. Cess et al presents a different justification for excluding high latitudes.

All in all the paper of Tsushima and Manabe leaves many questions unanswered as far as I can see. The comparison that has least problems concerns OLR only, where most models seem to have the wrong sign for the cloud radiative forcing.

I too have been studying the pnas paper by Tsushima and Manabe, and I find it fascinating if for no other reason than the fact that it shows us all how little is actually known about climate feedback factors, although, like Frank, I find the use of Hansen’s gain factor g something of a pain. (One has to keep in mind that g=1 means catastrophe while g=0 means lower climate sensitivity and g= -1 means little [but not zero] sensitivity.) The question in my mind has been whether increased radiative forcing and consequently increased temperatures could (via increased humidity) result in increased cloud cover and hence a reduced sensitivity. Fig. 2C says “no,” and the implication is that reduced snow cover trumps increased cloudiness (although the data scatter is large.) Fig 1C purports to show that albedo is reduced as surface temperature increases, but not one data point out of twelve touches the rms line within its error band.

I think the authors are correct in saying that the primary influence of their paper will be to provide a corrective to the models. That’s the best that can be done until we have satellite observatories with much higher accuracy, precision, and spatial resolution.

The paper does not claim to present anything more than some tests of the ability of the models to describe seasonal variability and the role of clouds in that. A good GCM type climate model should definitely be able to describe correctly the seasonal variability, seasonal variability is important enough to justify that requirement. Thus the test is of some significance.

Whether a model that describes seasonal variability correctly has the correct feedbacks for global warming is another issue that cannot be answered by this analysis. The only clear conclusion is that a model that fails badly on seasonal data cannot be correct for correct reasons on longer term data either. (It may succeed accidentally, but not for the correct reasons.)

What you said is true, Pekka, except that at the bottom right of page 7569 the authors themselves make the comparison between seasonal and long-term climate sensitivity. This sensitivity is, in my opinion, probably too high, because we are already (logarithmically speaking) half way to CO2 doubling but haven’t seen the anticipated temperature rise. I’m wondering why.

Aerosols, with each modeler getting to choose how strong the effect is. /sarc Quasi-cyclic behavior as exemplified by the AMO index is a better explanation, in my opinion. That does a much better job of explaining the relatively rapid increase in temperature in the first half of the twentieth century followed by the decrease between the mid 1940’s and the 1970’s.

They make the comparison, but that should be taken literally as it’s stated, i.e. noting that the numbers are not very different, not as claim that this analysis confirms the validity of the models in making long term projections.

Pekka and Peter: There is no data about the ability of models to reproduce AMPLITUDE of seasonal/annual global temperature change. They simply observed the changes in outgoing radiation associated with whatever annual temperature change the model produced. They didn’t show us the scatter in that relationship or clearly explain what CMIP data they actually used. Their earlier paper (ftp://luna.atmos.washington.edu/pub/breth/CPT/tsushima-etal-climdyn2005.pdf) has more details, but here they were using AMIP-I models, which specify 10 years of historical SST and ice coverage and allow the atmosphere to evolve. (As I understand it, energy is not conserved in AMIP-I models because SSTs are pre-set and not changed by incoming SWR and incoming and outgoing LWR.) Presumably these models got the amplitude of the global cycle roughly right since 2/3rds of the planet was being forced with historical data. Two of the three models used in that earlier paper had almost all of the feedback in the SWR channel, suggesting that water vapor/lapse rate feedback in the model is less than commonly believed.

The following passages seem to support some of our thoughts about the later paper

“Our analysis indicates that the [observed] solar gain factor (fS) is 0.32, which is smaller but is comparable in magnitude to the longwave gain factor (fL). Preliminary analysis reveals that this positive feedback effect is attributable in no small part to the albedo feedback effect involving snow and sea ice, which reflects a large fraction of incoming solar radiation. In addition to the albedo feedback, a component of the water vapor feedback involving solar radiation may have a small but significant positive feedback effect.”

“It is likely that the solar gain factor of the feedback for the annual variation differs substantially from the gain factor for the global warming. This is because the annual variation of surface temperature is practically zero in low latitudes, and is much smaller than the annual variation in high latitudes, where the albedo feedback involving snow and sea ice operates. On the other hand, the increase in surface temperature obtained from a global warming experiment has a significant magnitude in low latitudes, though it is smaller than the increase in high northern latitudes. We therefore believe that the change in reflected solar radiation per unit change of the global mean surface temperature is larger by a factor of 2 for the annual variation than for global warming. This implies that the gain factor of the annual variation may be twice as large as that of global warming.”

It’s too bad they didn’t look at how the results varied by latitude.

I’ve tried to find useful info on how well seasonal variations are reproduced by climate models. Seasons are a massive forcing on a local, rather than global, scale. Being local, energy from that forcing can flow elsewhere besides space. Outside the tropics, do observed and modeled relative humidity stay constant as the temperature warms by 5-15 degC? Does heat penetrate and leave the ocean as observed by ARGO? Is the amplitude of the seasonal change produced by models at various latitudes about right? Are observed changes in the lapse rate reproduced? The first step in most studies involves calculating temperature anomalies, so huge seasonal changes that dwarf long-term climate change can’t be seen. The annual cycle averaged over the whole planet is 5X bigger than observed warming so far.

Considering that models are essentially useless for regional climate variation, I would be very surprised if the latitudinal variation looks much like the real world. If I remember correctly, cloud cover distribution in models isn’t much like the real world.

The problem is that high latitude cloud cover turns out to be quite important, especially in the Arctic where most of the projected warming from doubling CO2 is supposed to happen ( see for example: http://www.nature.com/ngeo/journal/v4/n11/full/ngeo1285.html ). Due to the low angle of incidence of sunlight for most of the year, there may not be all that much difference between water and ice. Cloud cover, particularly mixed phase clouds, could have a bigger effect.

Unfortunately some of the specialized journals (including Geoscience) published by Nature are among the few interesting journals for which I don’t have access through university library. Thus I cannot find the full manuscript. The abstract fits well with my own prejudice, which tells that the importance of inversion leads to the situation where temperature changes are generally larger in Arctic than elsewhere for most causes of the change.

I realized that the Bitanja et al paper can be found through Google Scholar.

While their argument seems sound, I don’t like always the way they formulate their conclusions. In particular I dislike the statement of the abstract (a similar one is in the main text):

the additional radiation that is generated by the warming of these layers is directed downwards, and thus amplifies the warming.

They do certainly know that radiation from any single layer is equally strong up and down, but their formulation appears to contradict that. What they must mean is that less of the extra radiation escapes at TOA than reaches the surface, but why don’t they say that? Their last paragraph where conclusions are presented is also confusing at several points. It’s difficult to judge what some of their sentences are supposed to tell.

There was a strong inversion before the increase in CO2. After the increase the inversion is less strong as the surface warms more than the upper levels of the troposphere, but an inversion remains. This is both to be expected and observed as shown by the Fig. 6f of the Chung et al paper for the winter months. 925 hPa is mostly within the inversion layer in Arctic winter. The temperature at 925 hPa seems also to rise essentially as much as the surface temperature shown in Fig. 2j although the shapes of the curves are not identical.

With the low moisture of the Arctic winter atmosphere the direct influence of more CO2 is enhanced compared to other latitudes. Water vapor content remains low but is increased. That adds to the effect. My feeling is that Bitanja et al could have picked better illuminating results out of their calculations and they could have formulated their paper significantly better, but by these comments I don’t argue against their concrete results.

DeWitt and Pekka: There is considerable debate about the magnitude of various feedbacks: Will relative humidity stay constant? Is cloud feedback positive or negative? With the small increase in mean global temperature, the short period of semi-reliable observations from space, the changing biases in re-analyses, convincing answers are in short supply.

During seasonal warming, does relative humidity remain constant – or does warmth increase the height of convection, thereby decreasing relative humidity? With the large seasonal temperature swings that are repeated annually, there should be reliable data; but the answer will change from location to location. Pekka linked a paper i’m just beginning to read about seasonal cloud feedback (observations and models). Since the lifetime of water vapor in the atmosphere is about 9 days, clouds and water vapor should respond fast enough to stay in equilibrium with seasonal warming and cooling.

One can also check how well models reproduce season heat flux through the mixed layer.

DeWitt and Pekka: The Probst paper linked by Pekka above says that the observed cloud fraction (CF) in DJF minus the CF in JJA is positive (+5%) in 30-60 degN, which means that it is cloudier when it is cooler. It is slightly positive (+1%) in 30-60 degS, which means that it is very slightly cloudier when it is warmer. One might believe that it is much sunnier over warmer land and slightly cloudier over warmer ocean in the temperature zone. Perhaps rapidly rising, but narrow convective towers form over land during the summer, leaving a larger fraction of the sky for slowing descending (and therefore clear).

The seasonal cycle in the tropics is different – it is warmest in MAM, with a slight secondary peak in October, the difference in cloudiness between JJA and DJF is not a response to temperature change. One might expect cloudiness to follow the ITCZ. Not surprisingly 0-30 degN is much cloudier (10%) in JJA and 0-30 degS is much cloudier (9%) in DJF.

For 60S-60N, it is 1.5% less cloudy in JJA (when the planet as a whole is about 4 degC warmer) than in DJF.

The mean CF in the tropics is about 60%, 70% in 30-60N and 82% in 30-60 degS. Again, warmer means sunnier. The rapid updrafts of the ITCZ may produce a larger area of descending clear skies.

The average cloud cools the planet, but low clouds warm the planet and high clouds cool the planet. So we need to know more than just cloud fraction before we can legitimately say something about how cloud feedback changes with the seasons. Ramanathan’s chapter (Figure 5.6) has information about how cloud feedback changes dramatically with location. The clouds at 30-60S are the most effective at cooling the planet on the average. We want to know how cloud feedback changes with the season. The data is there to analyze

What if we assume the average cloud doesn’t change with the season? The average cloud fraction is about 66% while albedo is 30%, so a 1.5% reduction in cloud fraction might be converted to an 0.7% reduction in albedo or about +2.3 W/m2 for a 4 degK temperature rise. I think this is a fairly small feedback.

Most models predict a much lower CF than is observed. The seasonal and geographic distribution is bad too. The conclusion:

“Since most models are tuned to provide a TOA energy balance as close as possible to the measured record, the systematic deviations between a model and the CF observational dataset imply compensating deviations in a range of physical processes occurring almost everywhere in the system. The documented systematic inter-model discrepancies provide an indication of the effect of diverse mix of physical processes on CF. The authors believe that this is not an healthy situation.”

[…] reason for the difference is, I think, quite straightforward and is explained quite nicely in this Science of Doom post (H/T Pekka Pirila). It’s also essentially explained in Steve McGee’s post, but he […]